BEIRUT, Dec 12 (Reuters) - Five pro-Syrian Lebanese Shi'ite Muslim ministers and an ally of the president said on Monday they were suspending participation in the cabinet after it voted to call for a U.N. inquiry into a series of political killings.

Prime Minister Fouad Siniora had called for the urgent session hours after the killing of anti-Syrian lawmaker and newspaper magnate Gebran Tueni in a car bomb in Beirut. "This is not a resignation from the government but a suspension of membership in the cabinet while awaiting a decision from our political leadership," Hizbollah Energy Minister Mohammed Fneish told reporters. "We object to the principle of internationalising all Lebanese files ... and abandoning (Lebanon's) sovereignty," he added.

BEIRUT, Dec 13 (Reuters) - It has become all too familiar in Lebanon. An anti-Syrian politician or journalist is killed, condemnations pour in from friends and foes alike, the funeral attracts thousands, while officials urge unity. Yet the longer a U.N. inquiry into the murder of ex-Prime Minister Rafik al-Hariri drags on, the more every assassination threatens to rekindle sectarian divisions between the mostly Shi'ite Muslim supporters of Damascus and its Christian, Sunni and Druze opponents.

On Monday, Gebran Tueni, a newspaper magnate and staunch critic of Syria's erstwhile domination of Lebanon, became the third Lebanese to be killed in a car bombing since the truck bombing that killed Hariri and 22 others on Feb. 14.Three others, including Tueni's uncle the Druze Telecoms Minister Marwan Hamadeh, have barely escaped with their lives.

All of those killed since Hariri have been Christians who helped lead popular protests and lobby international pressure for Syria to withdraw its troops from Lebanon in April.