Syrian President Bashar al-Assad would be excluded from the transitional unity government proposed as part of a new United Nations peace plan for the country, William Hague said yesterday.

Speaking a day after a meeting in Geneva called by the UN-Arab League envoy Kofi Annan, which proposed the new plan, the Foreign Secretary said the transitional government should be made up of “people from the present government and opposition groups on the basis of mutual consent, which would of course exclude President Assad”.

He also admitted that he found the continuing conflict in Syria “deeply frustrating” in an interview for BBC1's Andrew Marr Show.

He did not elaborate on how a deal excluding Assad would be struck.

Fighting within Syria continues to escalate with the opposition claiming that 800 people have died in the last week and reports of serious fighting and heavy civilian loss of life in Douma, an opposition stronghold on the outskirts of Damascus.

Syrian opposition groups rejected the new UN peace plan yesterday and pledged not to negotiate with President Assad or any of his “murderous” regime.

The new proposals put the onus on Russia and China to persuade Mr Assad to leave power, but they are unclear about his future role. As a transitional authority could only be formed by “mutual consent”, each side has a veto on the other taking part.

“Every day I ask myself, do they not see how the Syrian people are being slaughtered?” a Syrian opposition leader, Haitham Maleh, told a new agency. “It is a catastrophe, the country has been destroyed, and they want us then to sit with the killer?”

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

Speaking from Cairo, where opposition groups are to meet today, he added: “…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.“

Bassma Kodmani, a Paris-based spokesperson for the fractious main opposition group, the Syrian National Council, said the agreement is “ambiguous” and lacks a mechanism or timetable for implementation.

In practice, the Syrian opposition remains too divided politically and militarily for now to establish a transitional government. There are believed to be at least 100 militia groups fighting the government, some of them receiving significant supplies of weapons from outside the country.

The Syrian government did not comment on the new version of the Annan plan, but Mr Assad has repeatedly said his government will eliminate terrorists and will oppose any foreign imposed type of government. It still controls the main population centres in Damascus and Aleppo, the main roads and is bombarding insurgent-held districts in other cities and towns.

Meanwhile, Turkey scrambled fighter aircraft to the border with Syria yesterday after Syrian helicopters flew close to its northern frontier, as military tension increases between the two countries.

A Turkish military statement claimed the helicopters had come close to the border on at least three occasions. Turkey said earlier that it would treat any Syrian aircraft approaching its frontier as a potential threat after one of its F-16 fighters on a reconnaissance mission was shot down on 22 June. The helicopters came within four miles of frontier yesterday the military statement said.