U.N. Secretary-General Ban Ki-moon said Monday the Syrian government is responsible for guaranteeing U.N. observers full freedom of movement to monitor the country's tenuous cease-fire, which appeared to be unraveling as regime forces pounded the opposition stronghold of Homs, activists said.
Even though overall violence in Syria has dropped significantly since the truce took effect Thursday, the government's shelling of the central city of Homs over the past four days has raised doubts about President Bashar Assad's commitment to special envoy Kofi Annan's plan to end 13 months of violence and launch talks on the country's political future.
An advance team of six observers arrived in Damascus late Sunday to negotiate the mission's ground rules with Syrian authorities.
Ban, speaking to reporters in Brussels, called on Assad to ensure the observers' work is not hindered.
"It is the Syrian government's responsibility to guarantee freedom of access, freedom of movement within the country," he said.
He called the cease-fire "very fragile," but said it was essential that it hold so that an "inclusive political dialogue can continue." He said opposition forces "should also fully cooperate."
The U.N. plans to increase the advance team to 30 people, all of them unarmed, Ban said, adding that the Security Council is expected to authorize a formal monitoring team of about 250 people later this week.
The advance team, led by Moroccan Col. Ahmed Himiche, met Monday with Syrian Foreign Ministry officials to discuss ground rules, according to Annan's spokesman, Ahmad Fawzi.
Assad's regime could try to create obstacles for the U.N. team. The failure of an Arab League observer mission earlier this year was blamed in part on regime restrictions imposed on the monitors, including having to travel with government minders.
Fawzi said in a statement issued in Geneva that the mission "will start with setting up operating headquarters, and reaching out to the Syrian government and the opposition forces so that both sides fully understand the role of the U.N. observers."
"We will start our mission as soon as possible and we hope it will be a success," Himiche told The Associated Press in Damascus.
A spokesman for the U.N. peacekeeping department, Kieran Dwyer, said an important priority for the observers in the coming days "will be to get out of Damascus and visit other centers, begin to decide where other operational bases will be established, and make contact with all side in those cities and towns."
He emphasized the need for the observers to be able to move freely and speak to anyone they wish "...without that person suffering negative consequences."
The international community hopes U.N. observers will be able to stabilize the cease-fire, which formally took effect Thursday. Annan will travel to Doha, Qatar, on Tuesday to take part in an Arab League meeting to discuss Syria.
But violence has continued in pockets throughout the country, fueling doubts about Assad's intentions.
U.S. ambassador to the U.N., Susan Rice, said ongoing violence contradicts the Syrian government's commitments and said its continuation "would call into question the wisdom and the viability of sending in the whole monitoring presence."
Activists reported government attacks in a number of places Monday.
Tarek Badrakhan, an activist from the battered Homs district of Khaldiyeh, said the regime resumed its intense bombardment of the neighborhood.
"The shelling hasn't stopped for one minute since this morning. There are buildings on fire right now," he said via Skype.
Badrakhan and other activists said the army appeared to be pushing to take control of the last rebel-held districts in Homs and was pounding Khaldiyeh from three sides. He said half of the nearby district of Bayada fell under the army's control Sunday night. Troops were trying to storm Qarabees and Jouret al-Shayah but the Free Syrian Army is repelling them, he said, referring to the army defectors fighting the government.
In activist videos posted online, shells could be heard whizzing through the air before smashing into residential areas in at least two Homs neighborhoods.
"We hope that the observers would come to Homs as soon as possible because if things go on like this, there won't be anything left called Homs," Badrakhan said.
Two activist groups, the Local Coordination Committees and the British-based Syrian Observatory for Human Rights, said at least four people were killed in shelling in Homs and in the nearby town of Qusair. Six people were killed in gunfire in the central city of Hama and four in the northern city of Idlib.
The Syrian leader accepted the truce deal at the prodding of his main ally, Russia, but his compliance has been limited. Assad apparently fears losing control of a country his family has ruled for four decades. Rebel fighters have also kept up attacks, including shooting ambushes.
The U.N. Security Council approved the observer mission unanimously on Saturday.
It's the first peace initiative to enjoy broad backing, including from Russia and China, who shielded the Syrian regime from Security Council censure in the past.
Associated Press writers Albert Aji in Damascus, John Heilprin in Geneva, Don Melvin in Brussels, Ibrahim Barzak in Gaza City, Gaza Strip, and Edith M. Lederer from the United Nations contributed to this report.