| BEIRUT/ISKENDERUN, Turkey
BEIRUT/ISKENDERUN, Turkey Rebel forces attacked Syria's main court in central Damascus on Thursday, state television said, while Turkey deployed troops and anti-aircraft rocket launchers to the Syrian border, building pressure on President Bashar al-Assad.
A loud explosion echoed through the streets and a column of black smoke rose over Damascus, an Assad stronghold that until the last few days had seemed largely beyond the reach of rebels. State television described it as a "terrorist" blast.
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.
The fighting coincided with a Turkish military buildup on its border with Syria and a growing sense of urgency in Western- and Arab-backed diplomatic efforts to promote the idea of a unity government to end 16 months of bloodshed.
But Assad himself 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. No one knows how to solve Syria's problems as well as we do," Assad told the state television channel of Syria's ally Iran.
He said Turkey's official stance belied the Turkish people's "positive view" of Syria.
A first substantial convoy of about 30 Turkish military vehicles, including trucks loaded with anti-aircraft missile batteries dispatched from the coastal town of Iskenderun, headed towards the Syrian border 50 km (30 miles) away.
A Turkish official who declined to be named said he did not know how many troops or vehicles were being moved but they were being stationed in the Yayladagi, Altinozu and Reyhanli border areas.
A general in the rebel Free Syria Army said on Friday that Syrian government forces had amassed around 170 tanks north of the city Aleppo, near the Turkish border, but there was no independent confirmation of the report.
General Mustafa al-Sheikh, head of the Higher Military Council, an association of senior officers who defected from Assad's forces, said the tanks had assembled at the Infantry School near the village of Musalmieh northeast of the city of Aleppo, 30 kms (19 miles) from the Turkish border.
"The tanks are now at the Infantry School. They're either preparing to move to the border to counter the Turkish deployment or attack the rebellious (Syrian) towns and villages in and around the border zone north of Aleppo," Sheikh told Reuters by telephone from the border.
Last Friday Syria shot down a Turkish warplane over the Mediterranean. Turkish Prime Minister Tayyip Erdogan responded by ordering his troops to treat any Syrian military element approaching the border as a military target.
This could cover Syrian forces pursuing rebels towards the border, or patrolling helicopters or warplanes. Syria said at the weekend that it had killed several "terrorists" infiltrating from Turkey.
A Reuters reporter near the town of Antakya saw the Turkish convoy moving out of the hills and through small towns on a narrow highway escorted by police.
Another convoy left a base at Gaziantep and headed for Kilis province, the site of a large camp for Syrian refugees. Video from the DHA agency showed the group of about 12 trucks and transporters filing through the gates of the base.
David Hartwell, Middle East analyst at IHS Jane's, called the Turkish action a pragmatic response to the downing of the Turkish aircraft, which Syria says was flying low and fast in Syrian airspace. "Damascus has been warned once. I doubt there will be a second warning."
Turkey, in the front line of Western efforts to press Assad to step down, hosts 33,000 Syrian refugees near its southern border as well as units of the rebel Free Syrian Army (FSA).
Members of the FSA, talking close to the border, told Reuters they did not believe the Turkish deployments were on a large scale or aimed at any crossborder intervention.
"The Turks know that any large-scale military action would need international support," said a senior FSA commander who spoke on condition of anonymity.
Turkey has in the past spoken of opening a humanitarian corridor on Syrian soil if the refugee flow grew unmanageable or if the violence and killing became intolerable.
Wary of igniting a regional sectarian war, it insists this would be possible only with U.N. backing. Western- and Arab-backed efforts to forge a joint diplomatic approach with Russia have so far failed.
Thursday's attack in Damascus follows weeks of growing FSA pressure. Rebels stormed a pro-Assad television channel on Wednesday, and have also targeted police and security barracks.
Syria denies there has been a mass popular uprising against Assad and says that the rebels who have now largely taken over from months of unarmed anti-government protests are foreign-backed Islamist terrorists, including members of al Qaeda.
Assad told Iranian television that his government had a duty to eliminate these to protect its people, and that Washington was content for al Qaeda to attack countries it did not like.
"When you eliminate a terrorist, it's possible that you are saving the lives of tens, hundreds, or even thousands," he said.
NEW ANNAN PLAN
Diplomats at the United Nations say international mediator Kofi Annan will seek backing from the permanent members of the U.N. 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 Assad must step down but does call for a unity government that would exclude figures who jeopardize stability - a condition that many 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.
"This is just a new labyrinth. It is new silliness for us to get lost in, and haggle over who can participate and who can't," said Ahmed, an FSA fighter in Homs, epicenter of the revolt against four decades of Assad family rule in which more than 10,000 people have been killed, by a U.N. count.
An FSA member in Damascus added: "The FSA is doing its work, and it is not looking to the outside world. We don't want a transitional government unless it is the one formed by rebel military councils. The world is conspiring against the Syrian revolution."
(Additional reporting by Jonathon Burch and Jon Hemming in Ankara, Marcus George, Yeganeh Torbati and Zahra Hosseinian in Dubai; Writing by Ralph Boulton; Editing by Janet McBride, Kevin Liffey and Michael Roddy)