A showdown between government troops and opposition forces in Syria’s largest city, Aleppo, is “imminent,” the U.N.’s human rights office said on Friday, as the Red Cross said it is pulling some of its foreign staff from Damascus out of concern for the safety of its workers.

The country’s chaos has spread to Syria’s biggest cities in some of the most widespread and sustained violence the two areas have seen in more than 17 months of conflict. Rebels have been locked in fierce fighting with government troops in Aleppo for six days and are bracing for an attack amid reports that the regime is massing reinforcements to retake the embattled city of 3 million.

U.N. High Commissioner for Human Rights Navi Pillay said unconfirmed reports are coming out of the capital, Damascus, of extra-judicial killings and shootings of civilians during fighting in the city’s suburbs. Expressing deep alarm at the situation, Ms. Pillay said the report “bodes ill for the people of that city (Aleppo).”

“And it goes without saying, that the increasing use of heavy weapons, tanks, attack helicopters and reportedly even jet fighters in urban areas has already caused many civilian casualties and is putting many more at grave risk,” she said in a statement read to reporters by her spokesman Rupert Colville.

The statement also said that there have been clashes in Homs and Deir el-Zour.

A senior U.N. diplomat close to the mediation effort of international envoy Kofi Annan said they are “watching the situation in Aleppo with great concern.”

“The ground is shifting. We use words like ‘It’s fluid’ and it certainly is... It has been a roller-coaster ride,” the diplomat said, while speaking on condition of anonymity because of the delicacy of the negotiations among world powers on the U.N. Security Council.

Red Cross move

The International Committee of the Red Cross said on Friday it is temporarily moving some of its foreign staff from Damascus to neighbouring Lebanon. A Red Cross spokesman in Geneva, Hicham Hassan, said the move was prompted by security concerns but that a core team of about 50 staff would remain.

Syrian MP flees to Turkey

Turkey’s state-run agency said a Syrian legislator from Aleppo has fled to Turkey and also warned that Syria was preparing for a massive offensive on cities where rebels are fighting government forces. The Anadolu agency said on Friday that Ikhlas Badawi has defected in protest of the Syrian regime’s “violence against the people.”

She would be the first member of Syria’s Parliament to defect from the Parliament that was elected in May.

In January, Legislator Imad Ghalioun left the country to join the opposition, saying Syria was suffering sweeping human rights violations. He was from the city of Homs that was being subjected to a massive regime attack at the time.

On Friday, the Britain-based Syrian Observatory for Human Rights said troops bombarded the neighbourhood of Fardous killing at least four people. It added that Sunni cleric Abdul-Latif al-Shami was kidnapped and killed in Aleppo. It gave no further details, although some activists said al-Shami is a government supporter.

Mohammed Saeed, an Aleppo-based activist, said helicopters were bombing with heavy machine-guns rebel-held areas east and west of the city on Friday. He added that army reinforcements arrived in the city on Thursday and a major attack is expected any time.

Rami Abdul-Rahman, who heads the Observatory, said army reinforcements took positions around Aleppo. “I expect the attack to begin today,” he said.

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