China and Russia said Wednesday they were "decisively against" intervention or regime change in Syria as Arab and Western calls mounted for strong international action in the 15-month conflict.

The United States endorsed an Arab proposal to invoke the UN Charter's tough Chapter VII, while refraining from supporting its powers to initiate military intervention, as Secretary of State Hillary Clinton sought to mobilise support in Turkey.

Clinton, who has voiced mounting frustration with the Chinese and Russian positions, called on the international community to "close off the regime's economic life lines."

"The regime must end the atrocities, comply with all its commitments under the Annan plan and allow the transition to a democratic Syria to begin," she said.

As rebel fighters stepped up their attacks in and around Damascus, Clinton's Russian counterpart Sergei Lavrov warned regime change in Syria would lead the Middle East to "catastrophe."

Beijing and Moscow said after two days fo talks between Russian President Vladimir Putin and Chinese leaders that they strongly opposed intervention and regime change.

"Russia and China are decisively against attempts to regulate the Syrian crisis with outside military intervention, as well as imposing... a policy of regime change," a joint statement said.

Speaking in the Chinese capital, Lavrov urged the international community to resist calls from the exiled opposition to help oust President Bashar al-Assad's regime.

Opposition groups "outside Syria appeal to the world community more and more to bomb the Assad regime, to change this regime. This is very risky, I would even say it is a way that will bring the region to catastrophe."

Lavrov hit out at the rebel Free Syrian Army's announcement that it was no longer bound by a six-point peace plan brokered by UN-Arab League envoy Kofi Annan and endorsed by the UN Security Council in a resolution backed by both Beijing and Moscow.

The Russian minister proposed a high-level international conference with the participation of Iran among other powers.

Lavrov urged states with sway over Syria's opposition to convince it to stop escalating the situation, adding Moscow and Beijing would continue in lock step over the issue.

The two nations have vetoed two Security Council resolutions criticising Assad's regime, but they voted in support of Annan's blueprint to end the conflict, in which more than 13,500 people have died since March last year, according to the Syrian Observatory for Human Rights.

-- Assad risks 'genocide' --

The Annan plan was supposed to begin with a ceasefire from April 12 but as violence has raged on daily despite the deployment of nearly 300 UN observers, doubts have emerged about its effectiveness.

In the latest violence, rebels went on the offensive in and around Damascus, while 46 people were killed in shelling, blasts and clashes across the country, the Observatory said.

According to the Britain-based watchdog's figures, at least 168 soldiers have been killed in the past week, including 76 at the weekend.

Rebels clashed with regime troops in Harasta and at checkpoints near Douma, Irbin amd Zamalka, all in the Damascus region, among several other parts of the capital, said the Observatory.

In Latakia province, regime forces rained shells down on several villages and towns.

Clinton arrived in Istanbul to meet representatives of 15 Arab and European states to discuss how to halt the violence and remove Assad, ahead of a Security Council briefing by Annan on Thursday.

Washington gave its backing to an Arab League's proposal to invoke tough UN Chapter VII sanctions against Damascus -- without mentioning military intervention.

"We the United States hope that all responsible countries will soon join in taking appropriate actions against the Syrian regime, including, if necessary, Chapter 7 action in the UN Security Council, as called for by the Arab League last weekend," US Treasury Secretary Timothy Geithner said.

The United States was focused on boosting international economic sanctions against Syria "that can help hasten the day the Assad regime relinquishes power," Geithner said.

Assad appointed loyalist Riad Hijab as prime minister in a move France dismissed as a "masquerade."

Italy warned that Assad's policies risk creating "genocide" unless there is swift action to stop him.

Analysts said Syria risks descending into a long and bloody civil war with the Annan plan at a stalemate, the opposition badly fragmented and fierce resistance to any real changes by the Assad regime.

"I think you're going to find there'll be increasingly bloody episodes because the diplomacy has not managed to keep up with the situation on the ground," Salman Shaikh, director of the Brookings Doha Center, told AFP.

In Qatar, the newly founded Syrian Business Forum group of expatriate businessmen announced the creation of a $300 million fund to support the rebellion and said it planned to join the opposition Syrian National Council.

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