ALEPPO (Syria) - The Syrian army pressed its assault on rebels in commercial capital Aleppo on Sunday, while both sides reported atrocities and Arab foreign ministers postponed a planned meeting on the 17-month conflict.

The exiled opposition said that pro-government militia had summarily executed 10 civilians in a round-up in the flashpoint central city of Homs, while the official SANA news agency reported the murder of one of its staff, the latest in a series pro-government journalists to be killed.

The Arab League gave no reason for the indefinite postponement of its planned meeting in Saudi Arabia which had been due to discuss a replacement for international envoy Kofi Annan who announced his resignation earlier this month.

In Aleppo, troops shelled rebel-held districts as fighting flared anew around a southwestern neighbourhood that rebel fighters had quit last week, the Syrian Observatory for Human Rights said.

The Shaar, Tariq al-Bab, Sakhur, Hanano and Bustan al-Qasr neighbourhoods all came under bombardment, as the army pressed a ground offensive it launched on Wednesday to recapture areas seized by rebels since July 20, the Britain-based watchdog said.

In the capital Damascus, gunfire was reported in the Qadam neighbourhood.

Outside the capital, machinegun fire was heard in the town of Al-Tal, where 15 civilians were killed in shelling and clashes on Saturday.

They were among 148 people killed across Syria on Saturday -- 85 civilians, 20 rebels and 43 soldiers, the Observatory said.

The pro-government Al-Watan newspaper spoke of "foiled bids to break the calm in Damascus, which was cleansed of terrorist groups who terrified residents."

In Aleppo, the paper said that the army was poised to assault the Sukari neighbourhood in the south of the city, after its recapture of the nearby Salaheddin district on Thursday.

"The door to Sukari district, the second bastion of the armed men in Aleppo, is now open for the army," it said, adding that troops had "gained control of several axes, which would allow them to storm the area."

The opposition Syrian National Council and activist groups said that the 10 civilians were executed a round-up of military-aged men in the Shamas district of Homs.

"Militiamen detained nearly 350 people from the Shamas district, assembled them in a courtyard and executed 10 of them," activist group, the Syrian Revolution General Council, said.

"The fate of the nearly 340 others is unknown and we fear greatly that they have met the same fate as the 10 martyrs," the group added.

The opposition SNC issued a similar statement.

"Ten young men were executed in the Shamas neighbourhood of Homs city after the army and pro-regime gunmen stormed the area and rounded up 350 young people," it said.

The official SANA news agency said that the head of its home news department, Abbas Ali, was assassinated by an "armed terrorist group" at his home in Jdaidet Artuz outside the capital on Saturday evening.

On Friday, rebels abducted three state television journalists as they accompanied government troops operating near Damascus, the Syrian Observatory said.

It came after a bomb attack on state television headquarters wounded several people last week and after an Al-Qaeda linked group claimed the abduction and murder earlier this month of state television presenter Mohammed al-Saeed.

As speculation mounted over who will succeed Kofi Annan when he steps down as international envoy later this month, UN chief Ban Ki-moon called for a "flexible UN presence in Syria" even after the mandate of the troubled observer mission he set up expires.

"A continued UN presence in Syria that goes beyond our important humanitarian work would allow systematic and meaningful engagement with the Syrian stakeholders, inside the country," the UN chief said in a letter to the 15 members of the UN Security Council.

"Furthermore, a flexible UN presence in Syria would provide the UN impartial means to assess the situation on the ground," he added. "The UN cannot discontinue its support."

The observer mission mandate is set to expire August 19, after the council voted last month to extend it for a "final" 30 days.

The mission -- originally 300 military observers and now reduced by half -- was deployed in April to oversee a peace plan, which should have begun with a ceasefire that never took hold.

In mid-June, the observers suspended patrols as fighting intensified.

The Security Council is scheduled to debate the future of the UN mission on Thursday, but so far there is little consensus.

The United States has been especially sceptical about prolonging the observers' mandate yet again. Syrian ally Russia is calling for an extension, saying the observers must continue monitoring the military situation.

Diplomats at the UN say veteran Algerian diplomat Lakhdar Brahimi, a former top League official, has been tipped to replace Annan but there has been no official word.