BEIRUT - A Norwegian general charged with overseeing a shaky UN-brokered truce in Syria arrived in Damascus on Sunday, boosting a monitor mission that activists say has helped ease the violence in the city of Homs, hotbed of a 13-month uprising.In the capital, militants fired rocket-propelled grenades at the Central Bank building, causing slight damage, and wounded four police when they attacked their patrol, state television reported. Activists in Damascus reported explosions and gunfire.Syria's SANA official news agency said UN observers on Sunday toured the Khalidiya district of Homs, which endured weeks of shelling by government forces before the April 12 ceasefire.An activist in Homs, speaking via Skype, said violence had dropped sharply in the city since the observers deployed a permanent two-man team to the restive city last week."There are still violations, but the shelling and mortar fire has stopped," Karam Abu Rabea said. "We have insisted that the observers stay in Homs because we know if they leave (the attacks) will continue."He said the presence of the monitors on Saturday had allowed residents to retrieve three bodies that had previously been too risky to collect because of the threat of sniper fire.The lull had also enabled people to clear rubbish left to rot in the streets. "There is a danger of disease from the rubbish. Until now it was left in the streets," Abu Rabea said.39 more dead, says groupDespite the relative calm in Homs, the Syrian Observatory for Human Rights, a UK-based group tracking the conflict, said at last 39 people were killed across the country on Sunday, including civilians, security forces and rebels.Twenty-three civilians were killed, most of them shot by security forces in a single village in the central province of Hama, it said. Six rebel fighters were killed as well as seven members of the security forces - four of whom died when ammunition they were handling exploded.On Sunday an Islamist group called "al-Nusra Front" claimed responsibility for a suicide bombing that killed at least nine people in Damascus on Friday.Both sides have been accused of multiple violations of the ceasefire engineered by UN-Arab League envoy Kofi Annan.Under the deal, Assad's tanks and troops are supposed to return to barracks. Damascus says this has happened, although UN Secretary General Ban Ki-moon disagreed this week, saying he was "gravely alarmed by reports of continued violence.""The problem is whether the Syrian government will agree to us deploying our own assets," he said late on Sunday.Ban said Syria's UN ambassador had promised unconditional cooperation. But it was difficult to "give full credibility on their promise, because they have not kept their promises," he told reporters during a visit to Myanmar.Besides Homs, the UN has established permanent monitoring post in the cities of Idlib, Hama and Deraa.The presence of the monitors has emboldened thousands of protesters to resume demonstrations after weeks of military crackdown, but activists say Assad's forces have hit back.Security forces carried out house to house raids in the Damascus suburb of Irbin on Saturday, arresting demonstration leaders who welcomed the observers a week ago, two resident activists said.General Robert Mood acknowledged the huge task awaiting the planned 300-strong unarmed mission, which now has 30 people on the ground, but said he was confident it could make headway."We will be only 300, but we can make a difference," Mood told reporters on his arrival in the Syrian capital."Thirty unarmed observers, 300 unarmed observers, even 1,000 unarmed observers cannot solve all the problems," he said. "I call on everyone to help us and cooperate with us in this very challenging task ahead."The United Nations says President Bashar Assad's forces have killed 9,000 people during the revolt, the latest in a string of uprisings in the Arab world against autocratic rule.Damascus says 2,600 of its personnel have died at the hands of anti-Assad militamen, and has accused the United Nations of turning a blind eye to "terrorist acts" against security forces.