“It is regrettable that Iran has yet to reach agreement with the IAEA on a plan to resolve all outstanding issues,” the spokesperson told a news briefing at UN Headquarters in New York.

According to media reports, a leaked quarterly report from the IAEA notes that Iran has doubled the number of uranium enrichment centrifuges it has in an underground bunker.

Meanwhile, Iran has also yet to allow the IAEA to visit a military site at Parchin, where the agency suspects Iran carried out explosives testing that it is now working to cover up, which has “significantly hampered” the agency’s investigation efforts.

The Iranian nuclear issue was a topic of discussion in the UN chief’s various meetings in Tehran, where he attended the 16th Summit of the Non-Aligned Movement (NAM). The Summit, under the chairmanship of the Government of Iran, in the Iranian and drew representatives from its 120 members, as well as from various associated observer countries.

Iran’s nuclear activities have been of international concern since the discovery, in 2003, that Iran had concealed its nuclear activities for 18 years, in breach of its obligations under the Nuclear Non-Proliferation Treaty. Iran has repeatedly stated that its nuclear programme is for the peaceful purpose of providing energy.

In a statement in the Tehran summit Iran’s Supremem leader said: “I stress that the Islamic Republic has never been after nuclear weapons and that it will never give up the right of its people to use nuclear energy for peaceful purposes.” But Israel, the United States and their allies in Europe  believe Iran is developing atomic weapons.

In a meeting on Thursday, with the Iranian Foreign Minister, Aliakbar Salehi, Mr. Ban had shared his concern about Iran’s nuclear programme and underscored the importance of transparency in this matter, as well as the need for Iran to fully comply with the IAEA.

He added that he has condemned threats by any Member State to destroy or delegitimize another. “And I have reminded leaders here – and indeed throughout the region – to lower the volume and stop the provocation that can lead this area down a slippery slope of conflict. It is time for more reason and responsibility,” Mr. Ban said.

Ban’s remarks come after Iranian remarks earlier this month threatening Israel’s existence. Iran’s president Mahmoud Ahmadinejad called Israel a “cancerous tumour” with no place in a future Middle East, were “outrageous and hateful” while Iranian media had earlier reported that Iran’s Supreme Leader Ayatollah Ali Khamenei had said Israel would one day be returned to the Palestinian nation and would cease to exist.

The Iranian remarks come as a series of Israeli media suggest that Israel could attack Iranian nuclear facilities ahead of U.S. presidential elections in November.

Taking place in the capital, Tehran, and under the chairmanship of Iran, the NAM Summit will be held on 26-31 August, and is expected to draw representatives from its 120 members, as well as from various associated observer countries.

Over recent days, there have been media reports of calls, from Israel and the US, for Ban to boycott the meeting.

Earlier this month, Israeli Prime Minister Benjamin Netanyahu urged Ban to cancel his plans to take part in the Tehran summit, according to Israeli media.

Washington made clear last week that it also wants the UN chief to boycott the event, and on Wednesday the US State Department reiterated its misgivings, according to Reuters. 

Mr. Ban’s spokesperson said that the UN chief takes “seriously” his responsibility and that of the United Nations to pursue diplomatic engagement with all of the world body’s Member States, in the interest of peacefully addressing vital matters of peace and security.

“With respect to the Islamic Republic of Iran, the Secretary-General will use the opportunity to convey the clear concerns and expectations of the international community on the issues for which cooperation and progress are urgent for both regional stability and the welfare of the Iranian people,” the spokesperson said.

“These include Iran’s nuclear programme, terrorism, human rights and the crisis in Syria.”

Over the past weekend, Mr. Ban’s spokesperson said the Secretary-General was “dismayed” by recent remarks threatening Israel’s existence – attributed to Iranian President Mahmoud Ahmadinejad and Supreme Leader Ayatollah Ali Khamenei – and condemned the comments, which he described as “offensive and inflammatory.”

Iran says its nuclear program is peaceful, but Western powers and their allies fear it is aimed at developing atomic weapons. Iran has been hit with four rounds of UN Security Council sanctions for refusing to halt its nuclear enrichment program.

The agency has been seeking access to the Parchin site for months, which is at the centre of Western suspicions that Iran has been developing a nuclear weapons capability despite Tehran’s repeated denials, arguing the site was not linked to its nuclear programme so it has no reaosn to allow inspections.

Last month, the International Atomic Energy Agency (IAEA) said new satellite imagery of the Parchin base near Tehran showed that “extensive activities” where there had been “virtually” none for years, Reuters reported.

 This “could hamper the agency’s ability to undertake effective verification” of the site, the IAEA warned.

 The United States and European Union have already made clear they will pimpose tighter sanctions if Iran pursues uranium enrichment.

In a speech last week, Netanyahu said world powers must both beef up sanctions and demand an immediate end to all uranium enrichment by Iran, whose mid-level 20 percent purification has been the focus of earlier negotiations, Al Arabiya reported.

The Israelis have signaled that delaying Iran’s progress could justify a military strike.

The announcement comes in the wake of nuclear talks in Baghdad on May 23-24 between six world powers and Iran known as P5+1 (Britain, China, France, Russia and the United States plus Germany).

 Those talks collapsed but have agreed to meet again in Moscow on June 18-19, before an EU oil embargo against Iran comes into force on July 1.

Iran insists its nuclear programme is solely for civilian purposes.

The meeting of the IAEA’s 35-member board of governors will be held behind closed doors, starting Monday, and is due to go on all week.

“Definitely, the progress of talks will have a positive impact on negotiations between Iran and P5+1,” Amano said. His visit to Tehran came ahead of wider negotiations at a meeting in Baghdad between six world powers and Iran on Wednesday.

Amano’s one day visit which was the first since becoming the IAEA chief in 2009 focuses on getting Iran to agree to terms that will allow IAEA probes of suspect Iranian sites, including the Parchin military complex where the agency had reported suspicious activities in the past,  AP reported.

Iran has refuted such claims by Western nations that it is developing  nuclear weapons. It has repeadetly refused to provide the IAEA access to relevant sites, officials and documents for over four years.

Meanwhile, the U.S. Senate unanimously approved on Monday a package of new economic sanctions on Iran’s oil sector just days ahead of a meeting in Baghdad between major world powers and Tehran, Washington Post reports.

“Today the U.S. Senate put Iranian leaders on notice that they must halt all uranium enrichment activities or face another round of economic sanctions from the United States,” said Republican Senator Mark Kirk, in a statement.

JX Nippon Oil & Energy Corp, Japan’s top refiner, says it would not be able to carry on importing oil from Iran.

Kuwait and top exporter Saudi Arabia are the main beneficiaries of the fall in Iranian shipments, along with new suppliers such as Gabon, as Japan buys more oil for firing generators following last year’s nuclear disaster, according to Reuters.

Earlier this year, China halved imports of crude from Iran, while an Iranian official denied that, in a statement to Mehr news agency, today.

While India has leaped to the top of the list of Iran’s oil customers, overtaking China, in a first-quarter buying surge ahead of tighter sanctions against Tehran this summer, according to data published by a leading industry consultant.

Iran sells most of its 2.2 million barrels per day of oil exports in Asia, where China, India, Japan and South Korea make up its four biggest buyers.

The United States and Europe have imposed tighter sanctions on Iran in an attempt makes to force it to halt a nuclear program they fear will be used to make weapons, which Tehran denies.

The EU had been the second biggest buyer of Iranian oil after China and its embargo is a direct strike on the biggest source of export income for Iran, the second largest producer in the Organization of the Petroleum Exporting Countries (OPEC), Alarabiya reported.

Iraqi Prime Minister Nuri al-Maliki  arrived  in the Iranian capital Tehran for two days of talks ahead of a meeting next month in Baghdad on Iran’s controversial nuclear program, Iran’s state news agency IRNA reported.

Al-Maliki arrived in Tehran on Sunday and was welcomed by Iran’s Energy Minister Majid Namjou.

Maliki is expected to meet during his visit with Iranian President Mahmud Ahmadinejad, parliamentary speaker Ali Larijani, and chief nuclear negotiator Saeed Jalili.

The focus of talks was on bilateral, regional and international issues, and to “develop and strengthen bilateral ties,” IRNA reported.

Talks during Maliki’s visit are also expected to concentrate on economic and regional issues like the crisis in Syria.

It is the Iraqi premier’s first visit to Iran in nearly two years, and comes as Iraq is preparing to host Iranian officials and the P5+1 group of world powers(Britain, China, France, Russia and the US plus Germany) on May 23, for the next round of talks on Tehran’s controversial nuclear weapons program.

Iran and the P5+1 wrapped up the first round of talks in Istanbul, Turkey on April 14. Both sides characterized the talks as “constructive” and “positive.”

Meanwhile, Iraqi Foreign Minister Hoshiyar Zebari has also met with an EU delegation to talk about issues relevant to the upcoming meeting between Iran and the P5+1, according to a statement by Iraq’s Foreign Minister.