Turkey has started strengthening its defences along the border with Syria as a precaution against any further Syrian military threat, as fighting intensifies in Syria's north.

Turkey has deployed extra troops, tanks and missile batteries to bolster its defences in the wake of Syria shooting down a Turkish warplane last Friday.

The government in Ankara has given orders for troops to treat any Syrian threat at the border as a hostile target.

Earlier this week Turkish prime minister Recep Tayyip Erdogan branded Syria an imminent threat.

"Everybody should know that Turkey's wrath is just as strong and devastating as its friendship is valuable," he told a meeting of his parliamentary party.

The move is also a precaution against fighting which has intensified in Syria's far north in areas under rebel control.

More than 20 people were killed across Syria yesterday.

The worst violence was in the capital Damascus, where two car bombs exploded outside the main court building, the Palace of Justice.

A loud explosion echoed through the streets and a column of black smoke rose over the city, a stronghold of pro-government forces that until the last few days had seemed largely beyond the reach of rebels.

Dozens of wrecked and burning cars were strewn over a car park used by lawyers and judges.

The state news agency SANA said three people had been wounded by a bomb hidden in one of the cars.

New peace plan

World leaders are preparing to meet in Geneva tomorrow to discuss a new peace plan aimed at ending the conflict.

Diplomats at the United Nations say international mediator Kofi Annan will seek backing from the permanent members of the UN Security Council and key Middle East players on Saturday for a plan for a political transition in Syria.

They say the proposal does not stipulate that Mr Assad must step down but does call for a unity government that would exclude figures who jeopardise stability - a condition that may not be enough to convince opposition groups to participate.

"The proposal is still murky to us but I can tell you that if it does not clearly state that Assad must step down, it will be unacceptable to us," said Samir Nashar, an executive member of the international Syrian National Council.

Rebel fighters said there was no part of the plan they could accept, and that they had lost patience with Annan's efforts.

President Bashar al-Assad also dismissed the idea of any outside solution to Syria's crisis.

"We will not accept any non-Syrian, non-national model, whether it comes from big countries or friendly countries," he told the state television channel in Iran.

"No one knows how to solve Syria's problems as well as we do."

ABC/Reuters