Opposition activists accused Syrian troops of shelling two cities on Tuesday in a campaign to weaken forces fighting President Bashar al-Assad's government before a ceasefire deadline next week.
Rebel fighters also kept up their attacks, killing three soldiers in separate actions in northern Syria, activists said.
Assad has agreed to a ceasefire negotiated by international peace envoy Kofi Annan from April 10, the latest effort to end a year of bloodshed stemming from an uprising against his rule.
An advance team from the U.N. peacekeeping department is due in Damascus this week to see how observers can monitor the truce, Annan's spokesman said in Geneva.
But Syrian opposition figures as well as Western governments have made clear they are not convinced that Assad, who has failed to honour past commitments, would keep his word.
He is a liar, said Waleed al-Fares, an opposition activist in Homs, a city which came to symbolise the anti-Assad struggle as opposition-held areas endured weeks of bombardments and sniper fire.
Fares said Assad was playing for time to gain the upper hand over poorly armed rebel forces which have been driven from city strongholds in the past two months.
Targets in Homs were coming under shelling on Tuesday, he said. Another opposition activist, Mortadha al-Rashid, told Reuters from Damascus that the western border town of Zabadani was also taking a pounding.
The regime shows no signs of stopping. There are people being shelled in Zabadani right now, Rashid said.
In violence elsewhere, rebel fighters killed one soldier in a clash in northern Idlib province, according to the opposition Syrian Observatory for Human Rights, a British-based monitor which collates reports from inside Syria.
Armed men also attacked the home of a military director of logistics in Aleppo, killing two guards, the Observatory said.
France said it would hold a meeting in the next two weeks to discuss sanctions on Syria to ensure they are implemented ahead of the next Friends of Syria meeting due to be held in Paris.
Given the news that we're getting today of the ongoing crackdown in Syria, this commitment must begin now, Foreign Ministry spokesman Bernard Valero said.
There is a final date of April 10, but it's from now that Mr Assad must begin implementing the immediate measures he has committed to.
If the regime continues its refusals, its massacres, then it will be pouring scorn on and insulting the entire international community, he said.
The United Nations estimates Assad's forces have killed more than 9,000 people in the past year, while the government says about 3,000 security personnel have been killed by what it describes as foreign-backed gangs of terrorists.
The Syrian state news agency SANA said 10 soldiers and policemen were buried with honours on Monday.
Accounts of the violence can be difficult to verify because the Syrian government restricts access to Western journalists.
SANA said Foreign Minister Walid al-Moualem met the president of the International Committee of the Red Cross, Jakob Kellenberger, and agreed on a cooperation mechanism for humanitarian assistance.
It made no mention of the ICRC's call for a daily two-hour ceasefire to provide aid and evacuate the wounded.
TURKEY BLAMES U.N.
The opposition Syrian National Council has endorsed Annan's six-point peace plan but made no official comment on the April 10 ceasefire target. Rebels of the Free Syrian Army have said they will stop shooting if tanks and artillery withdraw from cities.
Turkish Prime Minister Tayyip Erdogan accused the U.N. Security Council of indirectly supporting the oppression of the Syrian people by failing to adopt a united stance on Syria.
In not taking a decision, the U.N. Security Council has indirectly supported the oppression. To stand by with your hands and arms tied while the Syrian people are dying every day is to support the oppression, Erdogan told members of his party.
Annan, who acts for the United Nations and the Arab League, told the U.N. Security Council on Monday he would have liked to see a ceasefire sooner. Some council members were concerned that the next week could be used to intensify army operations.
Annan's spokesman Ahmad Fawzi, speaking in Geneva, said the aim was to bring a complete end to hostilities by April 12.
A U.N. peacekeeping advance team was due in Damascus in the next two days to discuss the deployment of monitors, Fawzi said. A team of up to 250 unarmed observers is envisaged although it will require a Security Council resolution.
Syria's ambassador to the United Nations, Bashar Ja'afari, said Damascus would not take all the blame if the plan failed and Annan must also get the armed opposition to comply.
A plan wouldn't be successful unless everybody is committed to it, Ja'afari said in New York.
Many foreign governments fear the conflict could descend into a full-scale civil war and drag in other Middle East players if it carries on much longer.
But Arab League states have backed away from earlier demands that Assad - whose family has ruled Syria for four decades - step down immediately and are focusing on Annan's initiative, which imposes no conditions on the president.
(Additional reporting by Stephanie Nebehay in Geneva, Jonathon Burch in Ankara, John Irish in Paris; Editing by Alison Williams)