Turkish soldiers in a military vehicle patrol on the Turkish-Syrian border. Turkey sent anti-aircraft guns to the region after Syria shot down a Turkey military plane (Osman Orsal/Reuters)

Turkey scrambled six fighter jets after military helicopters from Syria flew within 6.4 kilometres of its border, the Turkish government said, further escalating tensions in the region.

The F-16 jets were responding to three incidents on Saturday, the statement said, although there had been no violation of Turkish airspace.

Last month, Syrian forces shot down a Turkish jet in the border area. Ankara responded by placing anti-aircraft guns along its border with Syria. The unarmed RF-4E reconnaissance jet was shot down 1.6 kilometres inside international airspace on June 22.

On Sunday, Syria's main opposition group said nearly 800 people have been killed in violence across the country over the past week, which saw some of the bloodiest violence since the uprising against President Bashar al-Assad began 16 months ago.

Khalil Al Haj Saleh, a member of the Local Coordination Committees activist network, said the 800 figure appears to be "realistic" in light of the past week's carnage.

Opposition activists groups say more than 14,000 people have been killed in the 15-month-old uprising against President Bashar Assad's authoritarian rule, or on average of about 900 a month. That would make last week's toll alone, tallied by the Syrian National Council (SNC), almost as high as the monthly average.

The cross-border tensions and the mounting death toll have added urgency to the diplomatic efforts at an international conference over the weekend aimed at stopping the bloodshed.

Show Assad the 'writing on the wall'

The conference in Geneva on Saturday accepted U.N.-brokered plan calling for creation of a transitional national unity government in Syria. But at Russia's insistence, the compromise agreement left the door open to Assad being part of the interim administration. It could also include members of Assad's government and the opposition and other groups. It would oversee the drafting of a new constitution and elections.

The U.S. backed away from insisting that the plan should explicitly bar Assad from any role in a new government, hoping the concession would encourage Russia to put greater pressure on its longtime ally to end the violent crackdown on dissent. U.S. Secretary of State Hillary Clinton insisted on Saturday that Assad would still have to go.

It is now "incumbent on Russia and China to show Assad the writing on the wall" and "help force his departure," she said. Russia and China have shielded Assad's regime from U.N. Security Council resolutions condemning the crackdown.

Syrian opposition groups rejected the U.N.-brokered plan. The SNC criticized it as too ambiguous, underlining the seemingly intractable nature of the conflict. The opposition called it a waste of time and vowed as they always do not to negotiate with Assad or members of his "murderous" regime.

"Every day I ask myself, do they not see how the Syrian people are being slaughtered?" veteran Syrian opposition figure Haitham Maleh asked. "It is a catastrophe. The country has been destroyed and they want us then to sit with the killer?"

Maleh described the agreement reached in Geneva as a waste of time and of "no value on the ground."

"The Syrian people are the ones who will decide the battle on the ground, not those sitting in Geneva or New York or anywhere else," he said by telephone from Cairo, where opposition groups are to meet Monday.