AP/ April 16, 2012, 7:13 AM

Syrian activists report new shelling on Homs upon arrival of United Nations monitors

Moroccan Col. Ahmed Himmiche, foreground, is flanked by other U.N. observers as he talks to journalists before leaving the Sheraton Hotel in Damascus, Syria, April 16, 2012. / AP Photo

Updated at 7:07 a.m. ET

(AP) BEIRUT - An advance team of U.N. observers was negotiating the ground rules with Syrian authorities Monday for monitoring the country's 5-day-old cease-fire, which appeared to be rapidly unraveling as regime forces pounded the opposition stronghold of Homs with artillery shells and mortars, activists said.

Even though the overall level of violence across Syria has dropped significantly since the truce took effect, government attacks over the weekend raised new 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.

U.N. Secretary-General Ban Ki-moon called the cease-fire "very fragile," saying it's essential it holds so "inclusive political dialogue can continue."

Speaking Monday in Brussels, Ban said: "Just any small, unintended gunfire may break all this very fragile process." He called on Syrian authorities to exercise maximum restraint and said opposition forces "should also fully cooperate."

Special Section: The Arab Spring
Syrian activists say cease-fire is collapsing
Advance team of U.N. observers arrives in Syria

The advance team of six U.N. monitors arrived in Damascus Sunday night. Annan's spokesman said the team, led by Moroccan Col. Ahmed Himmiche, met Monday with Syrian Foreign Ministry officials to discuss ground rules, including what freedom of movement the observers would have. Ahmad Fawzi said the remaining 25 observers are expected to arrive in the coming days.

The Security Council demanded full freedom of movement for the U.N. team, but the regime could try to create obstacles. The failure of an Arab League observer mission earlier this year was blamed in part on regime restrictions imposed on the observers, including having to travel with government minders.

"It is the Syrian government's responsibility to guarantee freedom of access, freedom of movement within the country," Ban said.

Fawzi said in a statement issued in Geneva on Monday 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," Himmiche told The Associated Press as he left a Damascus hotel along with his team Monday morning.

The international community hopes U.N. observers will be able to stabilize the cease-fire, which formally took effect Thursday, although pockets of violence have persisted, particularly in the central cities of Hama and Homs.

Tarek Badrakhan, an activist from the battered and almost deserted Homs district of Khaldiyeh, said the regime resumed its intense bombardment of the neighborhood early Monday for the third consecutive day.

"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 on a push 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.

"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, confirmed the intense shelling of Homs and said two people were killed in the city of Hama in central Syria on Monday when security forces opened fire on their car.

Western countries and the Syrian opposition are skeptical Assad will abide by Annan's six-point plan for a cease-fire and the weekend pounding of Homs along with scattered violence in other areas has reinforced those doubts.

Assad accepted the truce deal at the prodding of his main ally, Russia, but his compliance has been limited. He has halted shelling of rebel-held neighborhoods, with the exception of Homs, but ignored calls to pull troops out of urban centers, apparently for fear of losing control over a country his family has ruled for four decades. Rebel fighters have also kept up attacks, including shooting ambushes.

Syria's state-run newspaper Tishrin said Monday that Damascus is "satisfied" with the U.N. resolution to send observers to the country because it respects Syrian sovereignty. The paper added that the resolution says all parties were responsible for halting violence. "This is a clear cut international recognition of the crimes and assaults committed by armed groups," it said.

The U.N. Security Council approved the observer mission unanimously on Saturday. A larger team of 250 observers requires more negotiations between the U.N. and the Syrian government next week.

The secretary-general expressed serious concern with the Syrian government's continued shelling of Homs and said "the whole world is watching with skeptical eyes" whether the cease-fire can be sustained.

"It is important — absolutely important that the Syrian government should take all the measures to keep this cessation of violence," Ban told reporters after meeting Belgian Prime Minister Elio Di Rupo on Sunday.