Syrian troops and tanks battled rebels on Friday, opposition activists said, only four days before a troop pullback agreed by President Bashar al-Assad as part of international envoy Kofi Annan's plan to end a year of bloodshed.
The renewed violence erupted a day after U.N. Secretary-General Ban Ki-moon said the conflict was worsening and attacks on civilian areas persisted, despite assurances from Damascus that its troops had begun withdrawing under the plan.
Annan said both the government and opposition must stop fighting at 6 a.m. Syrian time on April 12, if Damascus meets its deadline 48 hours earlier to pull back troops from cities and cease heavy weapons use in populated areas.
But activists reported tank fire in at least three urban centers on Friday - the town of Douma near Damascus, the restive city of Homs and Rastan, north of Homs.
"Tanks went into Douma last night, then they left. Today at 7:00 in the morning they came back. There has been shelling on Douma since the morning. We are not sure if people were killed but the shelling did not stop," a local activist said.
"At least 5 tanks and 10 buses loaded with security men and Shabiha (pro-Assad militia) entered Douma," he said.
In Rastan, "the tanks began advancing in the morning, then the fighters from the Free Army went out and confronted them," said one activist. "They blocked the advance and the Assad army left. Then artillery started."
Accounts of the violence are difficult to verify because Syria's government restricts access to independent journalists.
Assad blames the unrest on foreign-backed "terrorists" and has put forward a reform program which includes holding a parliamentary election on May 7.
His opponents have dismissed Assad's reform pledges as an attempt to play for time, saying it is impossible to have a valid election amid continuing repression.
The British-based Syrian Observatory for Human Rights, a pro-opposition website, said troops were fighting Free Syrian Army rebels in Douma as well as in Rastan on the highway between Homs and Hama cities.
There were no immediate reports of casualties.
Demonstrations broke out in the eastern province of Hasakeh, in the town of Qamishli and Deir al-Zor city. Protesters carried the white and green rebel flag, some saluted other rebel cities.
Army shelling of villages in the northwestern province of Idlib has prompted a swelling exodus of refugees. Turkey said there were now 23,835 Syrian refugees on its territory.
Over 2,800 arrived on Thursday, a Turkish official said, more than double the highest previous one-day total.
They crossed close to the Turkish village of Bukulmez and more were waiting on the other side of the border, the official said. Forty-four minibuses ferried the arrivals from the border to a refugee camp at Reyhanli.
"The army is destroying buildings and bombing them till they turn to charcoal," said Mohammed Khatib, a refugee who said he came from Kastanaz, a Syrian town of 20,000 people.
"The army wants people to move out of their houses. If the residents refuse, they destroy them with the people inside."
More than 42,000 Syrians have fled their country since the revolt against 42 years of Assad family rule began a year ago. Loyalist forces have killed over 9,000 people, by a U.N. tally. Syria says 6,044 have died, including 2,566 soldiers and police.
Annan told the U.N. General Assembly by video link from Geneva that the Syrian authorities had told him this week troop withdrawals were under way in the towns of Deraa, Idlib and Zabadani. But he said he wanted "fuller information".
Western powers are not convinced Assad will honor the promised truce and believe he may seek loopholes giving him more time to cripple the Free Syrian Army (FSA) and deter protesters.
It is also uncertain whether the FSA has enough control over its fighters to enforce Annan's ceasefire deadline.
Syria's U.N. ambassador Bashar Ja'afari said the plan did not require any pullback of police - who have played a big role in the conflict as suggested by the state's own casualty toll.
Last year the opposition said troops had disguised themselves as police and repainted army vehicles in police colors before the arrival in December of Arab observers sent to monitor what proved an abortive Arab League peace plan.
A Norwegian general attached to U.N. peacekeeping arrived in Damascus on Thursday to examine prospects for an eventual U.N. ceasefire monitoring mission of up to 250 unarmed observers, something which would require a Security Council resolution.