BEIRUT - Opposition activists accused Syrian troops of shelling two cities on Tuesday in a campaign to weaken forces fighting President Bashar Assad's government before a cease-fire 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 cease-fire 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 UN 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.Turkey blames the UNThe opposition Syrian National Council has endorsed Annan's six-point peace plan but made no official comment on the April 10 cease-fire 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 UN 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 UN 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 UN Security Council on Monday he would have liked to see a cease-fire 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 UN 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.