Peace envoy Lakhdar Brahimi began a visit to Cairo, meanwhile, after issuing an appeal for a ceasefire during the upcoming Muslim holiday of Eid al-Adha.

The Syrian Observatory for Human Rights said the pre-dawn air raids around Maaret al-Numan were the "most violent" since insurgents captured the strategic Idlib province town last week.

The warplanes targeted the blockade of the highway to second city Aleppo, theatre of intense fighting for the past three months, it said, adding rebels responded with anti-aircraft fire.

Army shelling of nearby Kafr Nabal killed two children, aged six and 10, said the Observatory, adding they were among at least 70 people who died in bloodshed across the country.

Another five children under the age of six died along with two adults in shelling of homes at Mayadeen village in the eastern province of Deir Ezzor, added the Britain-based group.

"The army's bombardments are killing the future of Syria," Observatory director Rami Abdel Rahman told AFP.

The Observatory -- which relies on a network of activists, medics and lawyers for its information -- says children account for 2,300 of the 33,000 people killed in the conflict.

Forces loyal to President Bashar al-Assad are also battling rebels at Eastern Ghuta, in the countryside outside Damascus.

They pounded Jobar, a stronghold of dissent in the capital itself, and the towns of Harasta and Hammuriyeh to the east.

Brahimi, the UN-Arab League envoy for Syria, called for a ceasefire as he shuttled between Syria's neighbours, bitterly divided by the conflict along the confessional lines that have traditionally riven the Islamic world.

The Algerian veteran troubleshooter visited Shiite-majority Iraq after talks in Shiite-ruled Iran, closest ally of Syria's minority Alawite-dominated regime.

Last week, Brahimi visited Saudi Arabia and Turkey, the two Sunni-led states which have been the greatest champions of Syria's opposition. On Tuesday he was in Cairo where he met Egyptian Foreign Minister Mohammed Kamel Amr.

"Brahimi has appealed to the Iranian authorities to assist in achieving a ceasefire in Syria during the forthcoming Eid al-Adha, one of the holiest holidays celebrated by the Muslims around the world," his office said.

Heightened Turkey-Syria tensions

Eid al-Adha, which falls at the end of October, marks the climax of the annual hajj pilgrimage.

"He reiterated the call by UN Secretary General Ban Ki-moon for a ceasefire and a halt to the flow of arms to both sides. A ceasefire, he said, would help create an environment that would allow a political process to develop."

The escalation in Idlib province, which borders Turkey, came as a senior US official visited Ankara for talks on the conflict in Syria amid heightened tensions between the two neighbours.

"We continue to consult with our partners in the region including Turkey on a variety of issues related to Syria," US embassy spokesman in Ankara T.J. Grubisha told AFP.

Tensions between Syria and Turkey have soared as Ankara and Damascus banned flights from each other's airspace after Ankara confiscated a cargo of radar equipment from a Syrian flight from Moscow last week.

On October 3, five Turkish civilians were killed by cross-border fire against the rebels that Syria charges are receiving arms from Gulf Arab states through Turkey.

The United States has called on all Syria's neighbours to monitor their airspace carefully.

"Certainly we support the decision that Turkey has made in light of the apparent violation of their airspace by this aircraft," State Department spokeswoman Victoria Nuland said.

"We are encouraging all of Syria's neighbours to be vigilant with regard to how their airspace is used, particularly now that we have this concrete example."

A day after the European Union imposed a 19th round of sanctions on Damascus, Switzerland said it has blocked 100 million francs (almost $108 million, 83 million euros) in assets linked to the Syrian regime.

And the UN food agency said prices for basic provisions have nearly doubled in Syria since the conflict erupted, and that it has failed to deliver supplies to 100,000 people because of the spiralling fighting.

State news agency SANA said, meanwhile, that Syria will hold by-elections on December 1 to fill five seats in parliament, two of which became vacant when sitting MPs defected to the opposition.