Smoke billowing from the Damascus suburb of Douma during shelling by state forces Syrian forces were locked in fierce gunfights with rebels in one city and shelled another on Monday, just hours after the first UN peacekeepers arrived to oversee a truce aimed at ending a year of bloodshed.
President Bashar al-Assad\'s forces killed two civilians in the central city of Hama and were fighting rebels at Idlib in the northwest, while also shelling the flashpoint city of Homs, said the Syrian Observatory for Human Rights.
Since a UN-backed ceasefire came into force at dawn on Thursday, at least 41 people, mostly civilians, have been killed in violence that prompted UN chief Ban Ki-moon to urge Syria to ensure the truce does not collapse.
Both the Local Coordination Committees (LCC) activist network and the British-based Syrian Observatory said that intense shelling of Homs resumed this morning, for the third consecutive day.
\"Government forces trying to take control of Homs neighbourhoods are pounding the districts of Khaldiyeh and Bayada with mortar fire,\" the Observatory said.
Activist claimed at least 27 people were killed across the country on Monday, including nine in Hama and seven in Idlib.
A 70-year-old police officer, Ali Mohamed al-Turk, was allegedly found dead after being kidnapped. His corpse showed signs of torture, the LCC said.
The LCC also reported four deaths in Idlib province after tanks shelled the town of Saraqeb and government troops opened fire on civilians in Shohada Square in front of a museum in Idlib city.
It also claimed to have recorded separate deaths in Aleppo and Homs.
The reports cannot be independently verified.
Syria\'s state-run news agency SANA claimed attacks by \"terrorists\" had \"hysterically escalated\" since the start of the fragile ceasefire last week.
An activist in Homs, Waleed Fares, who is based in the north west district of al-Khaldiyed, told UK daily The Guardian that his area and the neigbhouring districts of al-Bayadah and Jouret al-Shayah had experienced shelling all Monday morning.
Last night tanks were heard shelling the old city, he added.
Fares said there had been no resistance from the Free Syrian Army. \"There is no fighting just howling rockets and missiles\", he said.
Asked about the arrival of the first team of UN peace monitors, Fares compared the initiative to the troubled mission of the Arab League monitors earlier this year. \"It has failed before, I hope [it] succeeds, but the regime is not [telling the] truth,\" he said.
\"They will see damaged buildings, they will see mothers who have lost their brothers, and their sisters and their sons. Homs is a very sad city ... the picture here in Homs is very very very bad,\" he said.
Syria\'s fragile ceasefire was tested on Sunday when the army repeatedly shelled the central city of Homs and rebels attacked a police station near Aleppo, compounding the job of the UN observers who landed in the country last night. Ahmad Fawzi, the spokesman for international mediator Kofi Annan, said the size of the monitoring group could eventually be expanded to 250.
An advance team of six international observers arrived in Damascus late on Sunday, the United Nations said.
The observers are being led by a Moroccan colonel Ahmed Himmiche.
\"We will start our mission as soon as possible and we hope it will be a success,\" Himmiche told AP as he left a Damascus hotel along with his team.
The delegation - the first of 30 monitors the UN Security Council approved on Saturday - will set up a headquarters and prepare routines so the mission can verify a cessation of hostilities is holding.
\"They\'ve arrived and they will start work (on Monday) morning,\" UN peacekeeping department spokesperson Kieran Dwyer said. \"The other monitors in the advance party are still expected in Syria in coming days.\"
 The next 25 would come from missions around the Middle East and Africa \"so we can move people quickly and they are experienced in the region,\" he told AFP.
Their mission is just one part of the six-point peace plan that Assad agreed with UN-Arab League envoy Kofi Annan.
The former UN secretary general wants more than 200 observers to be deployed in Syria, but the Security Council has said there would only be a full mission if the violence halts.
The government news agency SANA said Syria \"welcomes\" the observer mission, and hoped the monitors would see for themselves the \"crimes\" committed by \"armed terrorist groups.\"
They face a perilous task, with Western nations doubting the Assad regime\'s commitment to the ceasefire amid reports his forces have kept battering rebel strongholds and clashed with opposition fighters.
A spike in deadly violence forced the Arab League to end its own Syrian monitoring mission in late January, barely a month after sending them.
On Monday, security forces shot dead the two civilians when they opened fire on a car in Hama, said the Observatory.
Elsewhere, fierce fighting broke out at dawn between forces loyal to Assad and rebels in the city of Idlib, the Britain-based monitoring group said.
Regime forces resumed shelling rebel neighbourhoods of Khaldiyeh and Bayyada in the central city of Homs, a day after at least five civilians were killed there.
The authorities on Sunday charged that rebels had \"intensified\" attacks on security forces and civilians, warning of a response, as state media published a list of alleged acts of violence.
Security forces \"will prevent the terrorist groups from continuing their criminal attacks,\" said a military official quoted by state media, accusing the rebels of a deliberate escalation to wreck the truce.
Ban voiced concern over the shelling of Homs.
\"I am very much concerned about what has happened since yesterday and today,\" he said. \"It is important, absolutely important, that the Syrian government should take all the measures to keep this cessation of violence.\"
China and Russia, which raised earlier reservations over the text of the peacekeepers resolution and had vetoed past resolutions, backed Saturday\'s vote at the UN Security Council that approved the monitoring mission.
SANA reported, meanwhile, that foreign minister Walid Muallem would visit China at the invitation of his counterpart Yang Jiechi, to discuss Annan\'s mission.
UN Resolution 2042 approved the sending of 30 unarmed military observers as soon as possible and called on both Syrian government and opposition forces to halt \"armed violence in all its forms.\"
It also urged the government to \"implement visibly\" all its commitments under Annan\'s peace plan, including the withdrawal of all troops and heavy guns from cities.
The resolution\'s passage was welcomed by Syria\'s main opposition.
\"We are ready to act to make the Annan plan a success,\" the Syrian National Council said in a statement signed by its leader Burhan Ghalioun.
The United Nations says more than 9,000 people have been killed since the uprising began. Monitors say the death toll has topped 10,000.