Halki, born in 1964, is from the southern province of Deraa where the uprising against  Assad’s  rule erupted, replacing caretaker premier Omar Ghalawanji who was appointed hours after Hijab’s defection.

Like Hijab, Halki who belongs to Syria’s Sunni Muslim majority defected on Monday after only two month in office. Hijab fled to Jordan with his family.

The White House said the defection of Syrian Prime Minister Riyad Hijab shows that President Bashar al Assad’s government is “crumbling from within.”

Moreover, several Syrian diplomats have defected from Assad’s government in the recent weeks, including the ambassador to Iraq, the ambassador to UAE, the charge d’affaires in the UK where his first posting was in Greece as consul from 2003 to 2008, and the charge d’affaires in Cyprus.

The latest development came as battle raged between regime forces and armed rebels in the northern city of Aleppo. The rebel Free Syrian Army on Thursday pulled out completely from the embattled district of Salaheddin, in the northern city of Aleppo, a rebel commander said.

“We have staged a tactical withdrawal from Salaheddin. The district is completely empty of rebel fighters. Regime forces are now advancing into Salaheddin,” said Hossam Abu Mohammed, a Free Syrian Army (FSA) commander, according to AFP. 

“The fighters are withdrawing to Sukari district, where they are preparing a counter-attack,” he told AFP by telephone.

Day two of the most significant ground attack in Aleppo came as Syria’s key regional ally Iran prepared to host a meeting aimed at finding ways to end the ongoing conflict.

The reinforcements, which have been massing over the past two days, “have moved on the Salaheddin district, where the largest number of rebel fighters are based,” the Syrian Observatory for Human Rights said, according to Al Jazeera.

“The fiercest clashes of the uprising are taking place in several neighborhoods of the city,” the head of the Britain-based watchdog, Rami Abdel Rahman, told AFP.

Rebels in Aleppo, have been stockpiling ammunition and medical supplies in preparation.

Meanwhile, The United States said it feared a massacre in Aleppo after President Bashar al-Assad’s forces launched ground and air bombardments in preparation for a major onslaught against rebels in Syria’s commercial capital.

Even though the United States showed heightened concern over then in Aleppo on Friday, it rejected comparisons to a Libyan crackdown that triggered international intervention.

“We are very concerned about the situation in Aleppo,” White House spokesman Jay Carney said, condemning President Bashar al-Assad’s assault on civilians.

Ms. Pillay, the UN human rights chief also expressed particular concern about the likelihood of an imminent major confrontation in Aleppo, Syria’s second-largest city after the capital, Damascus.

Bernard Valero, a French foreign ministry spokesman, said yesterday that, “With the build-up of heavy weapons around Aleppo, Assad is preparing to carry out a fresh slaughter of his own people.

Al-Assad, meanwhile, is in the final preparations to launch a massive assault on Aleppo, Turkey’s Prime Minister Recep Tayyip Erdogan said on friday. “The regime is getting ready to mount an attack on central Aleppo with tanks and helicopters.” Prime Minister Recep Tayyip Erdogan warned that international organizations needed to take steps against Damascus amid Foreign Minister Ahmet Davutoglu’s suggestion that scenarios for a post-Baathist era were now on everyone’s table, according to Hurriyet daily.