UN-Arab League envoy Kofi Annan is calling on both Syria and opposition fighters to end the fighting with the goal of a "complete cessation" of violence by April 12.

Annan, who has proposed a six-point peace plan, said Thursday that daily levels of violence continue at an alarming level in Syria.

"We must silence the tanks, helicopters, mortars, guns and stop all other forms of violence, too — sexual abuse, torture, persecutions, abductions, destruction of homes, forced displacement, and other abuses, including on children," Annan said during a videoconference from Geneva.

The Syrian government has previously said that it will withdraw troops and heavy weapons from cities by April 10.

Annan said once the April 10 commitments are met, "all parties should move immediately to cease all forms of violence" with a view to  a "complete cessation" of violence by 6 a.m. local time on April 12.

"I urge the government and opposition commanders to issue clear instructions so that the message reaches across the country, down to the fighter and soldier at the local level."

Annan's plan requires regime forces to withdraw from towns and cities, followed by a withdrawal by rebel fighters. Then all sides are supposed to hold talks on a political solution.

Ahmad Fawzi, Annan's spokesman, told the Associated Press that Syria has told UN officials it is withdrawing troops from the southern province of Daraa, the northwestern province of Idlib and the mountain resort town of Zabadani, north of Damascus.

However, Fawzi also said he could not provide specifics on the claim.

"I really cannot go into details on the verification process, but what I can tell you is that we are looking at a range of sources and cross-checking that information carefully," he said. "The planning team now on the ground will not participate in any verification activities."

"The government has indicated that it will continue to update me on steps it is taking," Annan said during the videoconference. "But it is clear that more far-reaching action is urgently required."

Opposition skeptical

The opposition, however, is deeply skeptical that Assad will live up to his commitment to a truce and accuses him of trying to manipulate it to buy more time to continue his military crackdown on the revolt.

Mohammed Fares, an activist in Zabadani, denied claims that troops withdrew and said the army is still present in the town with checkpoints backed by tanks.

"Troops and tanks are in Zabadani and around it," he told the Associated Press by telephone.

Other activists reported attacks on both Daraa and Idlib on Wednesday. Activist groups reported more than 50 dead nationwide on Wednesday.

Douma-based activist Mohammed Saeed reported that troops shelled residential areas Thursday with tanks "in one of the most violent campaigns against the area since the uprising started." He said troops were using detainees as human shields as they marched into one of the suburb's main squares, a few miles northwest of Damascus.

"Soldiers in the Ghanam Square near the vegetable market were walking behind detainees," Saeed said via Skype. "They do that so that members of the Free Syrian Army do not open fire at the troops."

He said the shelling and clashes have been going on since 7 a.m. local time.   

"The regime has no limits in its crimes. They are ready to do anything," said Saeed. "They are hitting homes directly."

Another activist near Douma, Omar Hamza, said snipers took up positions on 20 buildings in and around Douma and opened fire at "anything that moved, even animals."

He said the shelling went on for eight hours, damaging homes and setting shops on fire. Hamza said the government appeared to be trying to put the heavily populated Douma under control before the ceasefire goes into effect for fear that there will be massive anti-government protests near the capital if regime troops withdraw.

Cities turned into "war zones"

UN Secretary General Ban ki-Moon said Thursday that there can be "no higher priority at this moment than stopping the bloodshed in  Syria."

"Cities, towns and villages have been turned into war zones," he said. "The sources of violence are proliferating. This is simply unacceptable, and must stop immediately."

Ban appealed to Assad and his government to "do what is right for the Syrian people" and urged the opposition to be ready to cease all violence according to Annan's plan.

"The future of Syria belongs to the Syrian people. We must do our utmost to safeguard their welfare and uphold their universal rights."

The UN estimates more than 9,000 people have been killed in Syria in the past  year. More than one million people inside Syria are in need of humanitarian assistance, Ban said, and thousands more have fled to neighbouring countries.

Also Thursday, a team from the UN peacekeeping department arrived in Syria to discuss how an eventual ceasefire monitoring mission might unfold, CBC's Melissa Kent reported from New York.

With files from The Associated Press and CBC's Melissa Kent