International envoy Kofi Annan says he's still hopeful that his peace plan will take hold and end the violence in Syria, despite continuing reports of shelling and deaths.

Speaking in Turkey after visiting a refugee camp on the Syrian border, the UN-Arab League envoy said there is still time for the fighting to end, but there must be no preconditions.

Military forces were supposed to withdraw from towns and villages on Tuesday, with both sides ceasing all hostilities by 6 a.m. local time Thursday.

Annan said Tuesday there have been indications of the government withdrawing from some areas, but he expressed concern over reports suggesting there have been military movement in some areas that hadn't been targeted previously.

"I believe it's a bit too early to say that the plan has failed," Annan said from Turkey. "The plan is still on the table, and it's a plan we are all fighting to implement."

Activists who supply much of the information coming from sites in Syria such as Homs, Hama and Idlib say Syrian army attacks have not diminished.

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UN-Arab League envoy Kofi Annan arrives at Yayladagi refugee camp in Hatay province on the Turkish-Syrian border. (Umit Bektas/Reuters)

In a letter sent to the UN Security Council, Annan said the security and human rights situation in Syria is unacceptable after more than a year of conflict.

"The scale of the suffering of the Syrian people is clear. A cessation of violence is urgent," he said in Tuesday's letter.

"It is essential that the next 48 hours bring visible signs of immediate and indisputable change in the military posture of the government forces throughout the country, as called upon by the six-point plan," the letter said.

Halt-violence deadline passes

Annan also said opposition members have indicated they would observe a ceasefire "provided Syrian forces withdraw from cities."

Syria, meanwhile, found itself increasingly isolated Tuesday, as the deadline passed for the country to halt the violence and meet the terms of the ceasefire agreed to by President Bashar al-Assad.

The country's main opposition group says 1,000 people have been killed by government forces in the last eight days. A spokeswoman for the Syrian National Council says troops loyal to Assad have intensified their onslaught in opposition areas. SNC spokeswoman Bassma Kodmani says 160 people were killed in Syria on Monday alone.

Kodmani told reporters in Geneva on Tuesday that regime forces have used heavy weapons, including anti-aircraft guns, against civilians. She says the humanitarian situation is "dramatically deteriorating."

Assad 'will be held to account'

U.K. Foreign Minister William Hague said his country continued to support Annan's efforts, but he issued a warning to Assad.

"We will be ready to intensify our support for the Syrian Opposition, and to support others seeking to do the same," he said in a statement. "And we will begin the process of seeking the referral by the Security Council of the situation in Syria to the International Criminal Court.

"President Assad and his closest cronies should be under no doubt that they will be held to account for their actions."

Peter Wittig, the German permanent representative to the UN, said Assad has not complied with the Annan plan, saying he instead scaled up the violence and the human rights violations.

"The human rights violations and the Syrian-provoked cross-border incidents also are serious escalations of the situation," Wittig said. "Assad continues to play tactical games. That has to stop."

Speaking in Moscow, Syria's foreign minister claimed opposition forces are violating the ceasefire. Russia and other key Syria allies, however, are clearly running out of patience, CBC Middle East correspondent Derek Stoffel reported.

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Pro-Syrian government demonstrators held a rally in Damascus on Saturday. (Bassem Tellawi/Associated Press)

"Bashar al-Assad has once again thumbed his nose at the international community," Stoffel said. "By now his troops and heavy artillery were supposed to be pulling out of residential areas across Syria. Instead this morning, Assad's forces continued to hit Homs, the city that has seen by far the most violence."

Syrian Foreign Minister Walid Muallem said Tuesday the government has already withdrawn some forces from some Syrian cities and that the UN-brokered ceasefire must start simultaneously with the deployment of the international observer mission.

"We have already withdrawn forces and army units from several Syrian provinces," Muallem said, following talks in Moscow with his Russian counterpart.

French Foreign Ministry spokesman Bernard Valero dismissed Syria's claims of compliance as "a new expression of this flagrant and unacceptable lie."

China urges peace

The Britain-based Syrian Observatory for Human Rights, an activist group, said there were no indications the Syrian regime was pulling back forces. Instead, the group and activists in Syria reported shelling attacks and raids in several locations in the north, centre and south of the country, it said.

"Soldiers are not being withdrawn from towns and villages," said Fadi al-Yassin, an activist in the Idlib province close to Turkey. "On the contrary, reinforcements are being sent."

Besides Russia, Syria's other major ally, China, said Tuesday it hoped the country would adhere to the peace plan.

"We hope that the Syrian government, opposition groups and other relevant parties concerned immediately and effectively respond to special envoy Annan's mediation plan, and hear the calls of the international community for a pragmatic commitment to abide by the promise of ceasefire and troop withdrawal," Reuters quoted a spokesman as saying.

With files from The Associated Press