Syrian forces have launched fresh military operations in several regions ahead of an April 10 deadline for the government to implement a peace plan brokered by U.N.-Arab League envoy Kofi Annan.
Activists say heavy shelling rocked the central city of Homs, the site of massive anti-government protests.
Rights groups and activists say at least 50 people were killed across Syria on Wednesday as a result of shelling and clashes between pro- and anti-government forces.
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The peace plan requires government forces to withdraw from towns and cities and observe a cease-fire. Rebel fighters are to immediately follow by ceasing all violence.
Also Wednesday, Russian Foreign Minister Sergei Lavrov warned Western and Arab nations against arming Syrian rebels. Speaking on a trip to Azerbaijan, Lavrov said "even if the Syrian opposition is armed to the teeth, it will not be able to defeat the Syrian army and the carnage will go on for years."
Lavrov also said a foreign military intervention would lead to even more disastrous consequences for Syria, which has seen a yearlong uprising against President Bashar al-Assad that has killed more than 9,000 people.
On Thursday, Annan is to address the U.N. General Assembly on the situation in Syria.
Middle East analyst Christopher Phillips said the government crackdown will likely to continue until April 10.
"Given the regime has taken a largely militaristic approach to this uprising, you suspect their intention is to continue to oppress and be relatively violent right up to the 10th deadline as a means to crush the opposition as best it can before that deadline comes about," Phillips said.
Phillips, an international relations lecturer at the University of London, said it is doubtful that Syria will uphold the provisions of Annan's peace plan.
"It's highly unlikely that he ((Assad)) will abide by the terms entirely. I think this regime has decided a long time ago that its best route for survival is the military option. Its acceptance of this plan appears to be a play for time as they have done in the past with other plans such as the Arab League plan," he said.
Some information for this report was provided by AP, AFP and Reuters.