Hizbullah and its allies boycotted the latest round of Lebanon's national dialogue on Thursday because of tensions surrounding a UN tribunal's investigation of the 2005 assassination of a former prime minister.Many fear there could be violence in coming months if the UN court probing the truck bombing that killed Rafik Hariri and 22 others indicts members of the militant Hizbullah, a Shi'ite force that accuses the tribunal of bias.Hizbullah's ally Michel Aoun said the boycott was to protest the government's refusal to tackle the issue of witnesses accused of giving false information to mislead the investigation.Seven out of 19 leaders were absent from Thursday's talks, which are part of a series of regular meetings held by Lebanon's political factions.Hizbullah shares power in a fragile unity government with a Western-backed coalition led by Prime Minister Saad Hariri — the son of the slain former leader.The bombing that killed Rafik Hariri along Beirut's Mediterranean waterfront on Feb. 14, 2005 was one of the most dramatic political assassinations the Mideast has seen. A billionaire businessman, Hariri was Lebanon's most prominent politician after the 15-year civil war ended in 1990.The tribunal has not yet indicted anyone in the assassination, but Hizbullah leader Sheik Hassan Nasrallah says he expects members of his movement to be named. That has raised fears of violence between the heavily armed Shi'ite guerrilla force and Hariri's mainly Sunni allies.Nasrallah also has called on the Lebanese to boycott the tribunal, claiming that all information gathered by it was being sent to archenemy Israel.Tensions in Lebanon have been high recently. Last week, a crowd of women attacked two UN investigators and a Lebanese interpreter as they gathered evidence at a private gynecology clinic in Beirut. The women scuffled with investigators and stole several items from them after the team arrived to go through phone records at the clinic.Hariri was a five-time prime minister who had close ties with Western leaders as well as Syria and was credited with helping rebuild Lebanon's capital after the country's 1975-1990 civil war. In the last few months before his assassination, however, he had tried to limit Syria's influence over Lebanon.Many Lebanese blamed Damascus for the killing, but Syria has denied having anything to do with the assassination. Hezbollah, which is backed by Syria and Iran, also denies any role.A wave of anti-Syrian protests after Hariri's killing led to the withdrawal of Syrian troops, ending almost three decades of Syrian domination of Lebanon.