The U.N. Security Council, including Russia and China, threw its weight on Wednesday behind efforts by Kofi Annan to end the bloody conflict in Syria, providing a rare moment of global unity in the face of the year-long crisis.

In a statement approved by all its 15 members, the council threatened Syria with unspecified further steps if it failed to comply with Annan's peace plan, which calls for a ceasefire and demands swift access for aid agencies.

Although the original statement was diluted at Russia's demand, editing out any specific ultimatums, the fact that all major powers signed up to the proposal represented a major blow to President Bashar al-Assad as he battles a popular uprising.

To President Assad and his regime we say, along with the rest of the international community: take this path, commit to it, or face increasing pressure and isolation, U.S. Secretary of State Hillary Clinton said in Washington.

At least 8,000 people have died in the revolt, according to U.N. figures. Violence has intensified in recent weeks as pro-government forces bombard rebel towns and villages, looking to sweep their lightly armed opponents out of their strongholds.

Syria lies in a pivotal position at the heart of a web of regional conflicts in the Middle East, comprising a mix of faiths, sects and ethnic groups, and diplomats fear the rebellion is degenerating into a full-blown civil war.

Assad's forces have chalked up a string of gains as they turned their firepower on areas held by rebels. But the fighting shows no sign of abating and analysts expect the insurgents to change their tactics and adopt guerrilla warfare.

HEAVY SHELLING

Opposition activists said the army used tanks, artillery and anti-aircraft guns on the Damascus suburbs of Harasta and Irbin early Wednesday, which were retaken from rebels two months ago but have seen renewed insurgency in recent days.

Elsewhere the army fired mortars into the Khalidiya district of Homs, while artillery targeted the rebel town of Rastan, north of Homs city, in central Syria. Video also showed shelling of the ancient Apamea castle at Qalat Mudiq, near Hama.

The British-based Syrian Observatory for Human Rights said two people died in the southern city of Deraa when the army opened fire after a bomb had hit a military convoy, killing two soldiers. It added that two girls died in gunfire in Qalat Mudiq.

The official Syrian news agency SANA reported the funerals of seven security force members killed in the fighting.

Reports from Syria cannot be independently verified because officials have barred access to rights groups and journalists.

Russia and China have vetoed two previous U.N. draft resolutions that would have condemned Damascus and have resisted calls from Western and Arab states for Assad to stand down.

But faced by growing global outrage at the bloodshed, the two countries agreed to a so-called presidential statement. They are generally non-binding documents but do require unanimous support in the Security Council.

Russia praised the document as pragmatic.

The most important thing is that there are no ultimatums ... and no suggestions as to who carries more blame, Foreign Minister Sergei Lavrov said during a visit to Berlin.

DEMANDS

The accord came a few days after Annan, a former U.N. secretary general, told the Security Council that Damascus's response to his plans for peace were disappointing and he had urged the international community to lay side its divisions.

His proposal, spelt out in the U.N. statement, tells the Syrian government to cease troop movements in population centres and end the use of heavy weapons in such areas.

It also calls for the government and opposition to hold talks to secure a peaceful settlement. Assad has not rejected the proposals but has challenged their feasibility and asked who can speak for the splintered opposition.

The Syrian opposition plans to meet in Turkey on March 26 to try to overcome their internal feuds and plot a more coherent strategy, sources said on Wednesday.

However, they have yet to agree on who should attend the gathering, underlining doubts about their ability to overcome their divisions, which have frustrated Arab and Western states seeking a reliable partner to unite the anti-Assad movement.

The Security Council last passed a presidential statement on Syria in August 2011, but council members did reach a rare agreement on March 1 to rebuke Damascus for not letting U.N. humanitarian aid chief Valerie Amos into the country.

Shortly after the Council approved those remarks to the press, Amos was allowed to visit Damascus.

Annan welcomed the U.N. support for his mediation efforts and called on Damascus to respond positively.

The latest Council accord came after Moscow had adopted a new, sharper tone with Syria, a long-time ally and home to Russia's only naval base outside the former Soviet Union.

We believe the Syrian leadership reacted wrongly to the first appearance of peaceful protests and ... is making very many mistakes, Lavrov told Russian radio on Tuesday.

France welcomed the Security Council's move and said Assad must now halt all violence and repression, allow humanitarian aid to reach everyone in need and engage in inclusive dialogue with the opposition to find a lasting political solution.

With this declaration the United Nations Security Council is beginning to take responsibility after months of blockage, French Foreign Ministry spokesman Bernard Valero said in Paris.

(Additional reporting by Louis Charbonneau in New York, Dominic Evans in Beirut, Steve Gutterman in Moscow, and Olivia Rondonuwu in Jakarta, Leigh Thomas in Paris; Writing by Crispian Balmer Editing by Mark Heinrich)