Barack Obama (right) and Vladimir Putin Syria\'s Local Co-ordination Committees (LCC) activist networks claimed 18 people were killed in Tuesday\'s violence, while troops pounded and raided several rebel bastions across the country. Clashes also erupted in Homs early on Tuesday, as two pipelines were attacked in the country’s east and north, a watchdog said.
 Regime forces clashed with armed rebels before dawn Tuesday in Homs where a soldier was killed amid “intermittent shelling” of several neighbourhoods of the central city, the Syrian Observatory for Human Rights said.
“Clashes took place this morning between regime forces and rebels in the vicinity of the Baba Amro neighbourhood which has been under regime control since last March,” the Observatory said.
The LCC, made up of anti-regime activists on the ground, reported that regime troops bombarded the Homs province town of Rastan with “fierce and continuous shelling since dawn.”
Rastan residents are facing food shortages and electricity is “completely cut off,” the LCC said.
Meanwhile, in the eastern city of Deir al-Zor, regime forces killed three civilians during raids in the Al-Jura neighbourhood, the British-based Observatory reported.
Elsewhere in Deir al-Zor, the oil hub of Syria, a pipeline was bombed, the watchdog said. An oil pipeline in Homs province was also attacked, it said but gave no further information.
In the northern city of Aleppo, one civilian was shot dead during the night as he participated in a demonstration, the Observatory said. Regime forces also carried out raids and arrests in Syria’s second city.
And in the northwest province of Idlib, violent clashes broke out between regime forces and rebels in a village on the Syrian-Turkish border. Local activists said government troops used artillery in the fighting.
The latest violence comes after dozens were killed on Monday, while according to the Observatory more than 14,400 people have died since the revolt against the regime of President Bashar al-Assad broke out in March 2011.
The Observatory says most of the dead are civilians, but it counts rebel fighters who are not deserters from the army as civilians.
Several children were reportedly among the victims of a Monday attack in the Damascus suburb of Douma.
Meanwhile, as reports of defections among high-ranking officials in the Syrian army emerged, US President Barack Obama and Russian President Vladimir Putin urged on Monday an immediate end to violence in the country.
But there was little sign the two powers had agreed a way to end the conflict.
The Al Jazeera news network on Tuesday reported that Adnan Sello, a leader of Syria\'sChemical Warfare Division, had defected and was now in Turkey.
Syria has one of the world\'s largest chemical weapon arsenals and a number of major chemical weapons complexes, some in areas of current conflict, such as Homs and Hama.
The bases are said to be guarded by elite forces, but whether they would stay at their posts if the Assad regime collapses cannot be predicted, reported the BBC.
Other videos posted on the internet claimed to show a number of top army officers announcing their defection to the Syrian opposition.
 In a joint statement following the first meeting with Obama since Putin returned to the presidency, the leaders said they shared a belief that Syrians should determine their own future.
The US and Russia have been at odds over how to resolve the Syrian crisis. The statement by both powers was made as Russia reportedly prepared to send two warships with marines to its naval base in Syria where UN monitors have suspended their patrols because of escalating violence.
“In order to stop the bloodshed in Syria, we call for an immediate cessation of all violence,” the two leaders said in a statement after meeting on the sidelines of the Group of 20 summit in Los Cabos, Mexico.
“We are united in the belief that the Syrian people should have the opportunity to independently and democratically choose their own future,” the leaders said.
Obama said he and Putin had pledged to work with “other international actors, including the United Nations, Kofi Annan, and all interested parties” to try to find a solution to the Syria crisis.
Putin said the two countries had found “many common points” on the 15-month-old uprising against President Bashar al-Assad in Syria.
The United States has voiced frustration at Russia’s blocking of UN Security Council moves against Assad. The head of the UN mission in Syria is to brief the Security Council on Tuesday on the deteriorating conflict.
The United States, Britain and France are working on a new UN Council resolution in which they want to threaten sanctions against Assad. But Russia, Syria’s main international ally, and China have already blocked two resolutions which just hinted at measures.
A British marine insurer, meanwhile, said it had cancelled cover for a Russian ship, the MV Alaed, following reports it was carrying Mi-25 helicopter gunships destined for Syria.
“We have already informed the ship\'s owner that their insurance cover ceased automatically in view of the nature of the voyage,” Standard Club said.
The Daily Telegraph reported that the ship was anchored off the coast of Scotland.
British Foreign Secretary William Hague on Tuesday announced that the ship had turned round and was heading back to Russia.
Moscow news reports, meanwhile, said Russia is preparing to send two amphibious assault ships and marines to the Syrian port of Tartus where Russia has a naval base to ensure the safety of its nationals.
Senator John McCain, who was defeated in 2008 by Barack Obama in his bid for the White House, accused the US president on Monday of failing to exercise leadership in the crisis and said Washington should rally a coalition that would conduct an air war in support of the rebels.
McCain renewed his accusations that Assad’s forces are increasingly deploying attack helicopters against rebels.
Regime infantry and snipers have given way to tanks, artillery and attack helicopters as Assad seeks to crush the uprising, McCain said in a speech at a Washington think tank, the right-leaning American Enterprise Institute.
“We are now seeing a rapid increase in Assad’s use of helicopter gunships,” he said.
“Whereas his forces once sought to clear and hold ground, they now appear to be under orders just to kill anyone and everyone they deem a threat.
“There’s every reason to believe that Assad will continue to escalate the violence, more massacres, more use of helicopters, and perhaps worse weapons after that,” he said.