BEIRUT -- Syrian artillery pounded the rebellious city of Homs and tanks and troops stormed towns in the north and south Wednesday, deepening doubts that President Bashar Assad will follow through on his commitment to a truce starting next week.

Anti-regime activists cited the new assaults as evidence Assad is trying to crush those seeking to overthrow his regime before the cease-fire brokered by international envoy Kofi Annan begins Tuesday. Activist groups reported more than 50 dead nationwide for the day.

Russia, a key Assad ally, warned other nations not to arm the opposition, predicting such a move would only increase bloodshed without ending Assad's rule. The international community is sharply divided over how to stop the violence that has left more than 9,000 people dead over the past year.

This week, Assad agreed to implement the cease-fire from April 10. The truce is the keystone of a six-point plan put forward by Annan, the joint U.N.-Arab League envoy. It 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.

A Syrian government official claimed Tuesday that troops had begun withdrawing from some calm cities while moving to the outskirts of tense areas. He gave no further details and spoke on condition of anonymity because he was not authorized to talk to the media.

But activists reached by phone Wednesday in north, south and central Syria said they had seen no sign that the military was pulling out. Some reported the opposite.

"They are still sending in reinforcements," Yazeed al-Baradan said in the southern town of Tafas. He said government tanks and armored cars pushed in early in the day, beefed up checkpoints around the city and torched more than a dozen homes of known regime opponents.

Another activist in the northern province of Idlib gave a similar report.

"We don't see any proof of withdrawals here," said Fadi al-Yassin. "Anyone who gives a promise to the U.N. that he will withdraw his troops has to show good intentions, but we know Assad has no good intentions. These are just maneuvers by the regime."

The opposition suspects Assad agreed to the truce plan just to buy more time to continue his military crackdown on the revolt.

Syria's uprising began in March 2011 when protesters inspired by other Arab Spring revolts took to the streets to call for political reform. The regime has tried to violently quash spreading dissent, and many in the opposition have since taken up arms to protect themselves and attack government troops.

But the local rebels fighting under the banner of the Free Syrian Army are outgunned by Assad's large, professional forces, and the failure of diplomacy to stop the violence has left many calling for arms.

"We have only one demand, and that is the arming of the Free Army," said al-Baradan, the Tafas activist. "Then, God willing, we will topple the regime ourselves."

A group of some 70 nations pledged this week to supply the opposition with aid and communications equipment, while Saudi Arabia and some of its Gulf Arab neighbors have started a fund to support rebel fighters. Much about the fund remains unclear, and any weapons reaching the rebels from outside Syria have yet to make a noticeable difference on the ground.

Syrian ally Russia warned that if other countries armed the opposition, it would exacerbate the conflict.

"Even if they arm the Syrian opposition to the teeth, it won't be able to defeat the Syrian army," Russian Foreign Minister Sergey Lavrov said. "The carnage will go on for many years."

Russia and China have resisted growing international calls for Assad to resign and have twice protected Syria from censure by the U.N. Security Council.

But both countries have endorsed Annan's plan, which does not call for Assad to leave power -- the uprising's central demand.

Most opposition figures dismiss the Annan plan as too little, too late.

Activists around the country reported government shelling, raids and gunfire that killed dozens of civilians and a number of rebel fighters and government soldiers.

Activist videos posted online showed explosions and columns of black smoke rising from the rebellious central city of Homs, apparently from government shelling.

The Britain-based Syrian Observatory for Human Rights said at least 28 civilians were killed in government attacks in Homs and nearby towns.

It said clashes between rebels trying to stop advances by government troops in the area left four opposition fighters and 14 soldiers dead.

The Observatory also reported government shelling and raids in Idlib and southern Daraa provinces as well as an explosion in Beit Saham near Damascus that killed seven people. The Syrian government reported seven dead and blamed the blast on "terrorists" preparing explosives.

The Observatory and another activist network, the Local Coordination Committees, put the day's death toll at more than 50.

Activists' claims could not be independently verified. The Syrian government rarely comments on specific incidents and has barred most media from working in the country.

Throughout the uprising, it has blamed the violence on terrorists serving a foreign conspiracy. It has yet to comment on the April 10 deadline, though Annan and Russian officials say it has accepted it.

The regime has accepted other peace plans in the past only to ignore them on the ground.

The violence has taken a high toll on civilians, and the International Committee of the Red Cross is pressing Syria to give aid workers access to embattled areas. The group's president, Jakob Kellenberger, visited Daraa province Wednesday with a team that distributed around 1,000 food baskets, said spokesman Saleh Dabbakeh.

Kellenberger has not commented publicly since he arrived on Monday.

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Associated Press reporters Albert Aji in Damascus, Syria, and Aida Sultanova in Baku, Azerbaijan, contributed reporting.