UN officials have denounced gross human rights violations by both sides in Syria, as fighting rages in the second city Aleppo with the army claiming to have secured much of a strategic district.
"Midan is under the control of the army," a military official told AFP Monday, a claim backed up by a correspondent on the ground.
The Syrian Observatory for Human Rights said at least four rebels were killed in fighting across the northern city, which has been the scene of battles since July 20.
In Geneva, the head of a UN commission investigating rights abuses in Syria said they had soared dramatically in recent weeks and that the UN Security Council should take "appropriate action" against war criminals.
"Gross violations of human rights have grown in number, in pace and in scale," Paulo Sergio Pinheiro said, adding that President Bashar al-Assad's regime -- and the rebels, to a lesser extent -- had committed war crimes.
"In a dramatic escalation, indiscriminate attacks on civilians in the form of air strikes and artillery shelling levelled against residential neighbourhoods are occurring daily," he said.
The indiscriminate use of weapons, he added, combined with a failure to protect civilians, reflected "a disturbing disregard for established rules of armed conflict."
Robert Serry, UN coordinator for the Middle East peace process, meanwhile told the Security Council that "indiscriminate shelling of civilian areas by government forces with heavy weapons, tanks and air assets has increased."
For its part, Human Rights Watch called on the Security Council to refer the situation in Syria to the International Criminal Court.
"This is one measure that all Security Council members, including Russia, should find it easy to agree on if they are truly concerned about the violations committed in Syria," the New York-based group's Nadim Houry said.
"Extrajudicial or summary executions of detainees in the context of an armed conflict are war crimes, and may constitute crimes against humanity if they are widespread and systematic," he added, in a statement.
In Cairo the foreign ministers of Egypt, Turkey and Iran met to discuss developments in Syria on the political and humanitarian fronts, the Egyptian foreign ministry said.
International peace envoy Lakhdar Brahimi, who also attended the Cairo talks, was set to visit the Altinozu refugee camp in Turkey's Hatay province near the Syrian border, a Turkish official said.
Brahimi said Saturday that the "crisis is dangerous and getting worse, and it is a threat to the Syrian people, the region and the world."
Turkey, which threw support behind Brahimi's mission, is already home to some 80,000 registered refugees in several camps in the southeast region bordering Syria, but has said it can handle no more than 100,000 refugees.
Meanwhile the German magazine Der Spiegel reported Monday that the Syrian army has tested a chemical weapons delivery system, firing shells at a research centre in its northwestern desert region. The periodical cited "witnesses."
"Five or six empty shells devised for delivering chemical agents were fired by tanks and aircraft, at a site called Diraiham in the desert near the village of Khanasir," east of the city of Aleppo, Der Spiegel reported.
The report referred to the Safira research centre, which is regarded as Syria's largest testing site for chemical weapons. It is officially referred to as a "scientific research centre."
Last month French President Francois Hollande warned that the use of chemical weapons by the Syrian regime would be a legitimate reason for a foreign intervention.
At least 64 people died nationwide on Monday, including 36 civilians, 15 soldiers and 13 rebels, the Britain-based rights observatory said, after 148 were killed the previous day.
Clashes erupted near a building belonging to the feared air force intelligence, and rebels attacked a military post in New Aleppo as fighting broke out in other parts of the city, the Observatory said.
The watchdog also reported that the army shelled the strongly pro-rebel district of Al-Hajar Al-Aswad in Damascus in preparation for storming it, with at least one person reportedly killed and several others wounded.
Shelling was also reported in several districts of the central city of Homs, which the army had claimed to have under its control.
In the northwestern province of Idlib, pro-regime gunmen killed three members of the same family in the town of Tamanaa, said the watchdog.
The death toll from the 18-month conflict has risen to more than 27,000 people, according to the Observatory, while the United Nations puts the figure at 20,000.
Iranian foreign ministry spokesman Ramin Mehmanparast meanwhile said Iran "does not have any military presence" in Syria, denying remarks by the head of the country's Revolutionary Guards, General Mohammed Ali Jafari.