The assassination of a pro-Syrian politician has heightened tensions in Lebanon, less than a week before talks begin aimed at reconciling deep divisions between the country’s rival factions.

Saleh Aridi, a senior member of the Lebanese Democratic Party, which is allied to the militant Shia group Hizbollah, was killed on Wednesday night when a bomb exploded as he started his car at his house in the mountains east of Beirut.

It was the first political assassination in Lebanon in almost a year but differed from previous attacks which targeted those opposed to Syria’s influence in Lebanon, including former prime minister Rafiq Hariri.

Aridi was a close adviser of Talal Arsalan, a Druze leader who is a minister in the new unity government, and had recently helped bridge differences among the Druze, a secretive Muslim sect that comprises about 10 per cent of Lebanon’s population.

Mr Arsalan on Thursday pointed the finger at Israel, which he said ”has an interest in igniting strife and exploding the internal situation” in Lebanon.

Lebanese leaders urged calm. ”We must beware of conspiracies aimed...at scuttling efforts toward reconciliation and preparations for national dialogue,” said President Michel Suleiman.

In Washington, Sean McCormack, state department spokesman, said the US was ’’deeply concerned’’ and said its support for the Lebanese government was ’’unwavering’’.

The attack has significant implications for Lebanon’s political stability, coming only one day after Mr Suleiman announced the resumption on September 16 of a ”national dialogue” aimed at forming a national defence strategy and defining the roles of the army and militias.

The talks are part of the peace deal reached in Qatar in May, after an 18-month political crisis that culminated in sectarian fighting between Hizbollah militants and pro-government Sunni and Druze factions, almost plunging Lebanon into a new civil war.

Sporadic fighting has continued between Alawites, a Shia offshoot with strong links to Syria, and Sunnis in the northern Lebanese city of Tripoli, but political leaders hope an accord signed on Monday will put an end to those clashes.

Particularly difficult discussions are expected next week over the fate of Hizbollah’s weapons.

The western-supported majority coalition wants the Shia group to be disarmed but Hizbollah, which is backed by Iran and Syria, says it needs to defend Lebanon against ”Israeli threats”. Hizbollah now leads the opposition in Lebanon’s national unity government.

Mr Suleiman, the former army chief appointed president as a result of the May talks, is considered uniquely qualified to preside over the talks, which will bring together leaders of rival factions.

”Suleiman is in a better position than anyone else to bring everyone together and start the discussion,” said one western diplomat in Beirut. ”And even a year ago these people would never even have been talking to each other.”

But the government has been playing down expectations of immediate progress.

”There are problems that we may not solve in one, two, three, four or even five sessions,” Tariq Mitri, information minister, told foreign reporters in Beirut this week. ”But [the fact there are talks] suggests we are developing the ways and means in which these problems can be addressed,” he said.