By Dominic Evans
BEIRUT, June 19 (Reuters) - Syrian forces bombarded the central city of Homs on Tuesday and clashed with rebel fighters shortly before the chief United Nations monitor was due to brief world powers on the escalating violence which forced him to suspend operations.
A resident in Homs said the sound of explosions could be heard across the city, and activists also reported shelling in the Damascus suburb of Douma and fighting between soldiers and rebels in northern Aleppo province near the border with Turkey.
The violence is the latest wave of relentless bloodshed which led United Nations observers - who were sent to Syria to monitor a ceasefire deal brokered by international mediator Kofi Annan - to halt operations on Saturday.
Norwegian peacekeeper General Robert Mood was due to brief the U.N. Security Council at 1900 GMT on the renewed violence, which he has blamed on both President Bashar al-Assad's forces and rebel fighters.
Alarmed but apparently impotent to resolve the crisis, the outside world is deeply divided in its response to an increasingly sectarian conflict which threatens to become a proxy war for regional powers.
Western nations and their Sunni Muslim allies in the Gulf and Turkey seek Assad's overthrow but are wary of intervention, while Russia, China and Shi'ite Iran - Assad's strategic ally - have protected Assad from a tough international response.
U.S. President Barack Obama and Russian President Vladimir Putin sought on Monday to find common ground over Syria when they met at a G20 summit in Mexico, but they offered no new solutions and there was no sign they had bridged their differences over imposing tougher sanctions on Damascus.
Activists say at least 2,000 people have been killed in Syria since Annan's April 12 ceasefire deal, intended to be the first stage in a political plan to resolve Syria's 15-month-old crisis, was supposed to put an end to the killing.
"There are many buildings and houses completely destroyed (in Homs), and many injuries in the field hospitals which need surgery," said one resident of Syria's third biggest city, who gave his name as Nidal.
"There are many martyrs and no medicine."
Mood said he was worried about civilians trapped in Homs after a week of trying and failing to get them out, and the Syrian Observatory for Human Rights said around 1,000 families were stuck there under fire from the army.
Syria said on Tuesday it had tried to make arrangements through the U.N. monitors for evacuations from Homs and blamed rebel fighters for obstructing those efforts and accused them of using civilians as human shields.
But Nidal blamed security forces, who he said opened fire on a Red Crescent vehicle as it tried to ferry people out of the centre of the city.
"Three days ago the regime suggested a ceasefire for two hours from 5 pm to 7 pm to move the residents from Old Homs and Jouret al-Shiyah districts," he said.
But when Red Crescent vehicles started the evacuation, "regime forces shot at the Red Crescent cars", forcing the aid organisation to call off the operation. He said only Assad's forces were operating in the area where the shots were fired.
Activists said violence flared across the country on Tuesday and state media said rebels blew up two oil pipelines.
SANA news agency said an "armed terrorist group" attacked a oil derivatives pipeline linking Homs and Damascus in the Sultaniya area of southern Homs, causing a fire and heavy smoke which residents said was visible from the centre of the city.
A crude oil pipeline in the eastern province of Deir al-Zor was also blown up. SANA quoted an oil ministry source say pumping was expected to resume in the next few days, adding that the same pipeline had been targeted twice in the last two weeks.
On Monday, activists said at least 79 people were killed across Syria, including 51 civilians and rebel fighters and 28 members of the security forces.
The United Nations says Assad's forces have killed more than 10,000 people in their crackdown on protests which erupted in March last year, inspired by uprisings across the Arab world, and slowly turned into an armed insurgency.
Authorities blame the violence on foreign-backed Islamists they say have killed more than 2,600 soldiers and police.
Russia supports Assad's argument that foreign-backed terrorists are behind the unrest and has repeatedly urged Western and Arab countries, who mostly back the rebels, to rein in their support in order to stem the violence.
Western powers in turn have criticised Russia over its arms supplies to Assad. A cargo ship now moving off the north-west coast of Scotland is believed to be carrying Russian weaponry to Syria, according to an insurer which says it has withdrawn coverage for the vessel.
Britain said it was aware of a consignment of refurbished Russian-made attack helicopters heading for Syria, but did not say if it was referring to the same vessel. (Editing by Angus MacSwan)