Ahead of his Tuesday meeting with President Assad, Annan appealed to the Damascus government to adhere to the terms of a cease-fire that appears to have been repeatedly violated since it was agreed early in April.

"I have come to Syria at a critical moment in this crisis," Annan said, as he joined UN observers in Syria on Monday.

"I urge the government to take bold steps to signal that it is serious in its intention to resolve this crisis peacefully, and for everyone involved to help create the right context for a credible political process."

Annan met Foreign Minister Walid al-Moallem on Monday as part of his efforts to rescue the six-point peace proposal. The former UN secretary-general condemned a massacre in the town of Houla, in which more than 100 people died.

"I am personally shocked and horrified by the tragic incident in Houla two days ago, which took so many innocent lives, children, women and men," Annan told reporters shortly after arriving in the Syrian capital.

Annan was just the latest international figure to express his horror at Friday's slaughter in Houla, which members of the UN observer team say killed 108 people and injured 300 others. They said their investigation found that artillery and tank shells had been fired into a residential area and that many of the victims were women and children.

Annan also used his statement to the press in Damascus to reiterate his demand that all parties to the Syrian conflict lay down their arms.

Friday's massacre, which was one of the worst single incidents since the conflict broke out early last year, appears to have sharpened the focus of diplomatic efforts to stop the fighting.

Security Council condemnation

Following an emergency meeting on Sunday, the UN Security Council issued a non-binding statement in which it condemned the killings in the "strongest possible terms."

Agreed by all 15 member nations, including Syrian ally Russia, it said the attacks on the residential area in Houla "involved a series of government artillery and tank shellings." It avoided specifying, however, who was responsible for the massacre.

The statement also repeated a call for the government to immediately withdraw heavy weapons from Syrian towns in line with Annan's peace plan.

Earlier on Monday, Russian Foreign Minister Sergey Lavrov discussed the Syria conflict with visiting British Foreign Secretary William Hague in Moscow. Speaking at a joint press conference, Lavrov said both Assad's government and rebels were to blame for the Houla massacre.

"We are dealing with a situation in which both sides evidently had a hand in the deaths of innocent people," Lavrov said. He added that he and Hague had agreed that pressure must be brought to bear on both sides to end the violence.

Hague stressed that both Britain and Russia supported Annan's peace plan as it was "at the moment the only hope" for putting an end to the crisis.

Fighting rages on

In Syria itself on Monday there was no sign of an end to the violence.

There were deadly clashes in several provinces including Idlib in the northwest and Daraa in the south, according to the London-based Syrian Observatory for Human Rights.

Demonstrators took to the streets in towns and villages across the country to protest against the massacre at Houla and the bombardment of the city of Hama, allegedly carried out by Syrian troops. The Observatory said 34 people were killed when Hama was subjected to random shelling by government troops on Sunday.

The government has denied any involvement in the Houla massacre.

"No Syrian tank or artillery entered this place where the massacres were committed," Foreign Ministry spokesman Jihad Makdissi told reporters in Damascus. "The soldiers didn't leave their places because they were in a state of self-defense."

Like most reports coming out of Syria during this conflict, it is virtually impossible to independently verify the events that happened in Houla and Hama, due to severe restrictions on foreign journalists working in the country.

pfd, rc/av (APE, AFPE)