Britain has formally recognised the newly formed Syrian National Council opposition as the sole legitimate representative of the Syrian people, as violence continued to rage across the country.
William Hague, British Foreign Secretary, told the UK parliament on Tuesday it was in the interests of Syria, of the wider region and of the UK that "we support them and deny space to extremist groups".
"Her Majesty's government has decided to recognise the National Coalition of Syrian Revolution and Opposition Forces as the sole legitimate representative of the Syrian people," he added.
Last week, France became the first Western nation to officially recognise the Syrian National Coalition, which was formed on November 11 in Qatar in opposition to President Bashar al-Assad.
Paris said it was now considering whether to arm Syria's rebels.
Britain said no option is off the table but Hague told parliament that no decision had been taken to supply arms to the Syrian rebels. The EU currently has an arms embargo on Syria.
On Monday, the coalition received an EU-wide recognition. Italy, Turkey and the Gulf Arab states have also recognised it as the sole representative.
Military base takeover
The US recognised the leadership body as a legitimate representative, but stopped short of describing it as a sole representative, saying the group must first demonstrate its ability to represent Syrians inside the country.
The latest development came as rebel fighters stormed an air defence base that Assad's military had used to bombard areas near the Turkish border. After taking over the base in the country's north, they carted off tanks, armoured vehicles and truck-loads of munitions.
Reporters from the Associated Press news agency, who visited the base late on Monday, saw the dead bodies of seven Syrian soldiers and rebels calmly searching buildings.
Meanwhile, Syrian government troops backed by tanks battled to oust rebel forces from the opposition stronghold of Daraya, a Damascus suburb, on Tuesday in some of the heaviest fighting in the capital for months.
They were met by fierce resistance from rebels, who hung on to their positions despite days of aerial bombardment, opposition sources said.
Also in Damascus, state television said that two mortar rounds struck Syria's information ministry building, causing some damage but no casualties.
Holding on to Damascus
Syrian TV blamed "terrorists" for the attack, referring to fighters who have been battling Assad's regime.
In-depth coverage of escalating violence across Syria
The rebels have been trying to take their 20-month-old revolt to the heart of Damascus, Assad's seat of power, and have gained footholds in its southern outskirts and in many surrounding suburbs.
On the international front, Turkish Foreign Minister Ahmet Davutoglu said NATO states had agreed to supply Turkey with a Patriot missile system to defend itself against Syrian cross-border shelling.
Although the deployment would be for defencive purposes only, it nonetheless marked a hardening in the foreign opposition to Assad.
In recent months, artillery and mortar fire from Syria have landed inside Turkey, increasing concern that the uprising could turn into a regional conflagration.