The Syrian military said on Friday that 10 personnel, including six pilots, were killed in an attack on an air force base and that the incident proved foreign involvement in the eight-month revolt against President Bashar al-Assad's rule.

The ambush -- the latest in a growing number of armed actions against the government -- took place on Thursday and was made public as international pressure grew on Assad to halt the crackdown on the uprising.

Earlier on Friday, a deadline set by the Arab League for Syria to sign a deal allowing monitors into the country expired without any government response. Turkey meanwhile said it could no longer tolerate any more bloodshed.

More than 3,500 people are estimated by the United Nations to have been killed since March, the majority of them civilians gunned down as they took to the streets of Syrian towns and cities to call for an end to Assad's rule.

Under an Arab League initiative, Syria agreed to withdraw troops from urban centres, release political prisoners, start a dialogue with the opposition and allow in monitors.

The bloodshed has continued and Arab foreign ministers had said in Cairo on Thursday that unless Syria agreed to the monitors, they would consider imposing sanctions including halting flights, curbing trade and stopping deals with the central bank.

The Assad government had not replied by the end of the deadline on Friday but an Arab source in Cairo said the League would wait until the day's end before deciding what to do.

OBLIQUE

But the announcement of the air force attack appeared to be an oblique response.

An armed terrorist group undertook an evil assassination plot that martyred six pilots, a technical officer and three other personnel on an air force base between Homs and Palmyra, a military spokesman said on state television.

This confirms the involvement of foreign elements and their support of these terrorist operations in an effort to weaken the fighting capabilities of our forces, he said.

The account fits the government narrative that it is facing an armed insurrection by trouble-makers backed by its enemies, rather than a largely peaceful pro-democracy movement inspired by the Arab Spring revolts which toppled the rulers of Tunisia, Egypt and Libya this year.

A Syrian opposition member told Reuters the attack was an ambush on a military bus near Furqlous, 35 km (22 miles) southwest of Homs.

Furqlous is a military region and it is not difficult for an insurgent guerrilla force to chose targets there, the source said.

In neighbouring Turkey, Foreign Minister Ahmet Davutoglu told a news conference on Friday he hoped the Syrian government would give a positive response to the Arab League plan.

If it doesn't, there are steps we can take in consultation with the Arab League, he said. I want to say clearly we have no more tolerance for the bloodshed in Syria..

The stepped-up pressure followed a French proposal for humanitarian corridors to be set up through which food and medicine could be shipped to alleviate civilian suffering.

But some a measure of comfort for Assad came from Russia, China and other countries, who expressed opposition to sanctions and warned against a foreign military intervention.

At the current stage, what is needed is not resolutions, not sanctions, not pressure, but internal Syrian dialogue, Russian Foreign Ministry spokesman Alexander Lukashevich said in Moscow.

Russia, a longtime ally, has urged Assad to implement reforms but has not joined international calls for his resignation.

Lukashevich said Russia supported the Arab League's call for a halt to the violence but that radical opposition groups with foreign support shared the blame. Outside military intervention was absolutely unacceptable.

After a meeting in Moscow on Thursday, diplomats from Russia, China and the other three emerging-market BRIC countries -- Brazil, India and South Africa - also warned against foreign intervention without U.N. backing.

A Western diplomatic source said the French plan, with or without approval from Damascus, could link Syrian civilian centres to the frontiers of Turkey and Lebanon, to the Mediterranean coast or to an airport.

Its aim would enable transport of humanitarian supplies or medicines to civilians.

French Foreign Minister Alain Juppe said the plan fell short of a military intervention but acknowledged that humanitarian convoys would need armed protection.

Of course...by international observers, but there is no question of military intervention in Syria, he told French radio.

The Arab League suspended Syria's membership two weeks ago, while this week the prime minister of Turkey - a NATO member with the military wherewithal to mount a cross-border operation - told Assad to quit and said he should be mindful of the fate of other fallen dictators.

The Syrian Observatory for Human Rights, a British-based opposition group, said at least 47 people were killed in Syria on Thursday, including 16 soldiers and 17 army deserters, mostly around the city of Homs and Rastan to the north.

Alongside the mainly peaceful protests, armed insurgents have increasingly attacked military targets in recent weeks. Officials say 1,100 members of the security forces have been killed since the outbreak of uprising.

(Reporting by Erika Solomon and Khaled Yacoub Oweis; Writing by Angus MacSwan)