Turkey will imminently lodge an official request with Nato asking the military alliance to deploy Patriot missiles along its border with Syria to guard against violence spilling over, a senior Turkish foreign ministry official said.

If approved, the deployment would represent a further deterioration in relations between Turkey and Syria - once close allies - and see more military hardware poured into a region where tensions are already high.

Britain also appeared to harden its stance on Syria on Wednesday when Foreign Secretary William Hague said he had ordered UK diplomats to talk directly to Syrian rebels. Britain's previous stance had been to engage only with political representatives of the opposition.

Syria's war, in which the opposition estimates 38,000 people have been killed, raises the spectre of wider Middle East turbulence and poses one of the greatest foreign policy challenges for U.S. President Barack Obama as he starts his second term.

Analysts said Obama had been unable to make bold moves on Syria during the election period because of the risk that doing so would hurt his popularity. Britain and Turkey have joined U.S. calls for President Bashar al-Assad to step down.

Syrian rebels fired mortars at Assad's palace in Damascus on Wednesday but missed, an attack underlining the growing boldness of those fighting to end his family's 42-year rule and the rebel strategy of launching high-profile attacks against symbols of his rule.

A July bomb that killed four of Assad's top lieutenants was swiftly followed up with an advance into Damascus by rebels but they were then partially beaten back by Assad's forces.

Damascus residents told Reuters heavy-calibre shells apparently aimed at the palace had hit the nearby residential Mezze 86 district that is home to members of Assad's Alawite sect. State-run media said at least three people had been killed and seven wounded in what it described as a terrorist attack.

The violence has highlighted the sectarian dimension of a civil war that is deepening the rift between Sunni and Shi'ite Muslims in the region - Assad's Alawite sect is an offshoot of Shi'ite Islam.

Allegations of Syrian soldiers looting foreign aid surfaced on Wednesday after a medical aid group said troops had been seizing the supplies and reselling them or channelling them towards government loyalists, putting millions of lives at risk.

"When the regime attacks one of our medical facilities, whether it's a hospital or something else, they load up everything they can carry, and they burn the rest," said Tawfik Chamaa, a Geneva-based doctor and spokesman for the Union of Syrian Medical Relief Organizations (UOSSM).

Direct contact with rebels

"(The armed opposition) are playing an increasingly influential role within Syria as the conflict worsens," Hague said in a statement.

"I have therefore now authorised my officials to have direct contact with an even wider range of representatives including military figures in the armed opposition."

He said Britain would continue to only supply non-lethal support to the unarmed opposition, in compliance with a European Union arms embargo and British export licensing laws.

British officials would stress the importance of human rights and the rejection of "extremism and terrorism", and contact with the rebels would be limited to political dialogue, he said. – Reuters