AMMAN - President Bashar Assad's forces fired heavy tank and rocket barrages at a Damascus suburb on Thursday, killing five people, opposition activists said, a day before a UN-brokered ceasefire is due to come into force.Meanwhile, United Nations war crimes investigators said they would seek a meeting with Assad. The team, led by Brazilian expert Paulo Pinheiro, has been gathering evidence and testimony for the past year on atrocities committed by Syrian government forces and armed rebels in the 19-month-old conflict. "We decided to send a letter to President al-Assad calling for a meeting ... it would be very important that he could receive us," Pinheiro told reporters.The fighting in Harasta, just northeast of Damascus, erupted after rebels overran two army roadblocks on the edge of the large town, which is on the main highway linking the capital to the country's north, they said."Harasta is being pummeled by tanks and rocket launchers deployed in the highway. The rebels are putting up a fight and it does not seem the army will be able to enter the town this time," Mohammad, a Damascus resident, said by phone.He was referring to the last armored incursion by loyalist forces into Harasta a month ago, which opposition campaigners said had killed 70 people.Harasta is one of a series of large Sunni Muslim suburbs ringing the Syrian capital that have been at the forefront of the 19-month-old rebellion against Assad.He belongs to the minority Alawite sect, an offshoot of Shi'ite Islam that has dominated Syrian politics since the 1960s.The Harasta Media Office opposition activists' group described the town as a "disaster zone" following the shelling."An (army) roadblock had been set up next to the main bakery. There is no water, no food, no medicine and prolonged power cuts," it said in a statement.Other residents of Damascus said the sound of shelling targeting Harasta and the nearby neighborhood of Zamalka could be heard from the center of the capital.On Wednesday, an Arab League mediator for the Syrian conflict told the U.N. Security Council that Assad has accepted a ceasefire for the Muslim 'Eid' holiday starting on Friday.An announcement by the Syrian authorities was expected later. But Moaz al-Shami, an opposition activist in Damascus said "no one is taking the ceasefire seriously"."How can there be a ceasefire with tanks roaming the streets, roadblocks every few hundred meters and the army having no qualms about hitting civilian neighborhoods with heavy artillery? This is a regime that has lost all credibility."