* Russia warns against unilateral U.S. action in Syria
* Army kills some 70 people in two-day assault on suburb
* Syria says foreign intervention "impossible"
* Five killed in neighbouring Lebanon in Syria-linked clash
By Dominic Evans
BEIRUT, Aug 21 (Reuters) - Russia warned the West on Tuesday against unilateral action on Syria, a day after U.S. President Barack Obama threatened "enormous consequences" if his Syrian counterpart used chemical or biological arms or even moved them in a menacing way.
Russian Foreign Minister Sergei Lavrov, speaking after meeting China's top diplomat, said Moscow and Beijing were committed to "the need to strictly adhere to the norms of international law ... and not to allow their violation".
The remarks were a reminder of the divisions hampering efforts to end the 17-month old conflict that increasingly sets a mainly Sunni Muslim opposition against President Bashar al-Assad's Alawite minority.
The United Nations says more than 18,000 people have been killed in a war which is affecting neighbouring states.
In Lebanon, at least five people were killed in sectarian violence linked to the Syria conflict, and Turkey, an opponent of Assad, investigated possible Syrian involvement in a car bomb that killed nine people on Monday.
Russia and China have opposed military intervention in Syria throughout the revolt. They have vetoed three U.N. Security Council resolutions backed by Western and Arab states that would have put more pressure on Damascus to end the violence.
After meeting Lavrov in Moscow, Syrian Deputy Prime Minister Qadri Jamil said Obama's talk of action against Syria was media fodder.
He said the West was seeking an excuse to intervene, likening the focus on Syria's chemical weapons with the run-up to the 2003 invasion of Iraq by U.S.-led forces and the focus on what proved to be groundless suspicions that Saddam Hussein was concealing weapons of mass destruction.
"Direct military intervention in Syria is impossible because whoever thinks about it ... is heading towards a confrontation wider than Syria's borders," he told a news conference.
In one of the latest battle zones, troops and tanks overran the Damascus suburb of Mouadamiya on Tuesday, the second day of an offensive to regain control of the area.
Activists said Assad's forces had killed at least 70 people in Mouadamiya since Monday. They included some two dozen men who had been executed and 16 people killed in a helicopter gunship attack on a funeral for victims of Monday's violence.
"The mourners set off with 19 bodies and came back with 35," Hayat, one of the activists said from the suburb.
Another resident, speaking to Reuters by telephone, said he had counted the bodies of some two dozen men who had been executed. "They were not killed by bombardment, their hands were tied and they were burnt and killed by knives," he said. Bodies were found in basements and looted premises, activists said.
State-imposed curbs on media made it impossible to verify the reports of the violence, which followed another bloody day on Monday, when about 200 people were killed across the country, according to the opposition Syrian Observatory for Human Rights.
An opposition group said Syria's air force had redeployed 30 Sukhoi fighter-bomber jets closer to cities where the army is battling to crush rebels in the north and east of the country.
The Soviet-era Sukhoi Su-22 planes, which can drop 400 kg (881 pound) bombs, flew from the Dumair and Sim air bases north and east of Damascus on Monday to bases in the city of Hama Tabaqa and Deir al-Zor, a senior official in the Higher Leadership Council for the Syrian Revolution said.
"This type of Sukhoi is more geared to bombing missions than aerial combat. They are now within a more manageable range to hit the cities of Aleppo, Homs and Deir al-Zor and areas in Idlib province," Mohammad Mroueh told Reuters from Amman.
The United States and its allies have shown little appetite for intervention to halt the bloodshed along the lines of last year's NATO campaign that helped topple Libya's Muammar Gaddafi.
But Obama used some of his strongest language yet on Monday to warn Assad not to use unconventional weapons.
"We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is (if) we start seeing a whole bunch of chemical weapons moving around or being utilised," he said. "That would change my calculus."
Syria last month acknowledged for the first time that it had chemical or biological weapons and said it could use them if foreign countries attacked it.
"We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people," Obama said, perhaps referring to Lebanon's Shi'ite Hezbollah group, an Iranian-backed ally of Assad, or to Islamist militants.
The U.S.-based Global Security website says there are four suspected chemical weapons sites in Syria producing the nerve agents VX, sarin and tabun. It does not cite its sources.
Israel, still formally at war with Syria, has also debated whether to attack the unconventional arms sites which it views as the gravest peril from the conflict next door.
Obama has been reluctant to embroil the United States in another war in the Middle East and refuses to arm Syrian rebels, partly for fear that some of those fighting the Iranian-backed president are Islamist radicals equally hostile to the West.
Rebels have seized swathes of territory in northern Syria near Turkey, which now hosts 70,000 Syrian refugees and which has suggested that the United Nations might need to create a "safe zone" in Syria if that total topped 10,000.
But setting up a safe haven would require imposing a no-fly zone, an idea which U.S. Defense Secretary Leon Panetta said last week was not a "front-burner" issue for Washington.
The Alawite-Sunni sectarian fault line flared in neighbouring Lebanon, where five people were killed and more than 60 wounded in the northern port city of Tripoli, a mainly Sunni city with a staunchly pro-Assad Alawite minority.
Gunmen in the Sunni district of Bab al-Tabbaneh and their Alawite rivals in Jebel Mohsen exchanged gun and grenade fire in sporadic fighting overnight and into the day, despite action by Lebanese army troops deployed in the port city, residents said.
The wounded included 10 soldiers, the army said.