Peace envoy Lakhdar Brahimi was to brief the Arab League on Monday on his mission to Syria that a rebel commander predicted is doomed to fail, as violence rattled Damascus and the second city Aleppo.

Also in Cairo, there were reports of a meeting of an unlikely quartet of Iran -- a strong ally of Bashar Al-Assad -- and Egypt, Saudi Arabia and Turkey, who have called for the Syrian president's ouster.

And the United Nations said human rights violations have soared dramatically in the Syrian conflict.

Brahimi was to brief Arab League chief Nabil al-Arabi on his visit to Syria, his first since taking on the job earlier this month, where he met Assad and members of the opposition tolerated by Damascus, a League official said. The UN-Arab League envoy and Arabi will discuss "the Arab and international moves required to resolve the current crisis in Syria," the official said.

Brahimi, who replaced Kofi Annan when he resigned over the failure of both sides to adhere to his six-point peace plan to which they had committed, said the "crisis is dangerous and getting worse, and it is a threat to the Syrian people, the region and the world."

After the veteran Algerian troubleshooter left Damascus on Sunday, a rebel commander said: "We are sure Brahimi will fail like the other envoys before him, but we do not want to be the reason of his failure."

Colonel Abdel Jabbar Al-Okaidi, the Free Syrian Army commander in Aleppo, said that he and other FSA officials had held an Internet conference call with Brahimi.

While Brahimi has insisted that "the solution can only come from the Syrian people," Okaidi accused the international community of "giving political cover to the regime." He accused world powers of pushing the opposition to sit down for talks with the regime but without pressuring the government to stop its repression.

"We are sure Brahimi will fail because the international community does not actually want to help the Syrian people," he told AFP by telephone. "We do not want the international community to help the Syrian people. We just want it to remove the political cover it grants to the criminal regime. We cannot be in dialogue with criminals."

In Tehran, the official IRNA news agency said the foreign ministers of Egypt, Iran, Saudi Arabia and Turkey were to hold their first high-level meeting on the 18-month Syrian conflict in Cairo on Monday.

Iran the previous day admitted for the first time that it has elite forces in Syria and in neighbouring Lebanon, where Pope Benedict XVI at the weekend added his voice to calls for an end to the bloodletting.

In a rare news conference, the commander of Iran's Revolutionary Guards said that members of his elite Quds Force were in Syria and Lebanon, but only to provide "counsel and advice."

Brigadier General Mohammad Ali Jafari said this did "not mean that we have a military presence there."

Western and Arab countries have accused Iran of giving military aid to Assad's regime.

Eighteen months into the crisis, the international community remains paralysed, with the West, Arab states of the Gulf and Turkey calling for Assad's removal, and Russia and China standing by its ally.

On Monday, Paulo Sergio Pinheiro, a top UN investigator, said in Geneva that "gross violations of human rights have grown in number, in pace and in scale" in Syria since a report issued last month.

The rights situation has "deteriorated to such a degree that it is difficult to describe," he told the 21st session of the UN's Human Rights Council.

On the ground, fighting raged in Syria's second city Aleppo amid a disputed claim that the army had managed to seize the strategic district of Midan from rebels, the Syrian Observatory for Human Rights said.

One battle broke out near a building housing the feared air force intelligence service, and rebels also attacked a military post in the New Aleppo area.

Pro-regime Syrian newspaper Al-Watan said the army had "cleansed" the Midan district, where the "majority of the armed men were (non-Syrian) Arab and foreign extremists." But Observatory director Rami Abdel Rahman said "clashes are ongoing in Midan and in several parts of Aleppo. Such claims are just part of the media war."

His Britain-based monitoring group said the army shelled the strongly pro-rebel district of Al-Hajar Al-Aswad in Damascus in preparation for storming it, reporting one person killed.

The latest violence came after at least 148 people were killed across Syria on Sunday, most of them civilians, according to the Observatory.

In addition, some 28 unidentified corpses were found across the strife-torn country, including 16 people who had been summarily executed in Qadam district of Damascus and 11 who had been shot dead in Kfar Sousa, also in the capital.

The death toll from the conflict has risen to more than 27,000 people, says the Observatory, which relies on activist accounts from the ground. The United Nations puts the figure at 20,000.