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. His comments were passed on to Reuters in neighboring Beirut.
"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.
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 the central city of Homs, speaking via Skype, said violence had dropped sharply 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.Snipers
Despite the relative calm, the Syrian Observatory for Human Rights, a UK-based group tracking the conflict, said two people were shot dead by snipers in Homs, and two others killed by security forces near Hama and the eastern city of Deir al-Zor.
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."
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.
BEIRUT (Reuters) -- 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 already helped ease the violence in the city of Homs, hotbed of a 13-month uprising.