Syria's regime unleashed tank fire and air strikes on rebels on Wednesday as it slammed France for recognising an opposition bloc formed in Qatar that it said amounted to a "declaration of war".

Tanks shelled two Palestinian refugee camps in the opposition bastion of southern Damascus, while fighter jets bombed Maaret al-Numan, a town near Turkey that rebels captured last month, a watchdog said.

But rebels killed at least 18 soldiers as they overran a military post near Ras al-Ain, a town also on the Turkish border that the armed opposition seized Friday, said the Syrian Observatory for Human Rights.

A day after France became the first Western nation to recognise the newly united opposition, Damascus hit out at the decision and said the Qatar meeting at which the dissident factions united on Sunday amounted to a war declaration.

"The Doha meeting was a declaration of war. These people (the opposition) don't want to solve the issue peacefully through the mechanisms of the UN," Syria's deputy foreign minister, Faisal Muqdad, told AFP.

"We read the Doha document and they reject any dialogue with the government."

Reacting to the French move, Muqdad said: "Allow me to use the word, this is an immoral position. They are supporting killers, terrorists and they are encouraging the destruction of Syria."

Prime Minister Dmitry Medvedev of Russia, a strong Damascus ally, also criticised countries siding with the opposition and insisted Moscow was staying neutral.

"We don't support anybody in this conflict, neither President (Bashar al-) Assad nor the rebels... but unfortunately, the point of view of some states is more one-sided," Medvedev told Finnish newspaper Helsingin Sanomat.

President Francois Hollande said Paris recognised the coalition as "the sole representative of the Syrian people and thus as the future provisional government of a democratic Syria, allowing an end to the Bashar al-Assad regime".

The question of arming the rebels would now "have to be necessarily reviewed not only in France but in all countries which will recognise this government," Hollande added.

National Coalition chief Ahmed Moaz al-Khatib has called on world powers to arm Assad's foes.

US President Barack Obama said on Wednesday Washington is encouraged by the new opposition coalition but is not yet ready to recognise it as sole legitimate representative of the Syrian people.

"We're not yet prepared to recognize them as some sort of government-in-exile, but we do think that it is a broad-based representative group," Obama told reporters at the first news conference after his re-election.

The Gulf Cooperation Council -- Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates -- has recognised the coalition, but the Arab League stopped short of doing so, only saying it saw the alliance as "the legitimate representative of the Syrian opposition".

On the ground, tanks moved on the Yarmuk refugee camp and the neighbouring Damascus district of Tadamum after battles in the area late on Tuesday, said the Observatory.

Shells struck a second refugee camp east of Yarmuk on Wednesday morning while fighter jets bombarded the Idlib province town of Maaret al-Numan, which rebels seized on October 9 and the army has since sought to take back.

The latest clashes, which killed at least 18 soldiers near Ras al-Ain, on the border with Turkey, also left dead three rebels and wounded other combatants, said the Observatory.

The insurgents have gained control of large swathes of territory in northern Syria, AFP journalists have observed, and it is possible to move freely for hundreds of kilometres (miles) making only small detours around army bases.

Syrian state television said "a military unit carried out an operation in Asfar Najjar in the area of Ras al-Ain to break a (rebel) cordon surrounding one of our military units."

That resulted in "the elimination of terrorists in the area and the destruction of their equipment and vehicles mounted with machine guns," it added.

A Syrian military source said the rebels had surrounded the base in the early morning.

"The army managed to break through the chain of rebels surrounding the base and escape," he told AFP on condition of anonymity. "After the rebels took full control the air force flattened the base."

A witness and a security source said rebels also made a strategic advance in the northern city of Aleppo, theatre of fierce clashes since July, taking a regime checkpoint at the north of the metropolis before dawn.

The Observatory has given an overall death toll of more than 38,000 since the revolt broke out in March 2011.

burs/bpz/al