“We demand the prime minister announce openly and clearly his commitment (to the tribunal) before Parliament on Tuesday and say that he will take all necessary steps to abide by its decisions, or get out, he and his government,” MP Fuad Siniora, himself a former premier and leading member of the pro-Western opposition, said.

Hezbollah’s leader denies his group had any role in Rafiq Harri’s 2005 killing and has vowed to protect suspects from arrest.

But the pro-Western bloc known as March 14 said in a statement that Hezbollah is holding the country hostage by making it choose between justice and stability. The Cabinet is packed with Hezbollah allies, so there is little enthusiasm within the current leadership to press forward with the case.

Mikati’s government, in which Hezbollah and its allies control the majority of seats, this week faces a vote of confidence in Parliament.

The UN-backed Special Tribunal for Lebanon last week issued an indictment in the 2005 assassination of Hariri along with arrest warrants for four senior members of Hezbollah.

The Special Tribunal, set up in 2007, has triggered a deep political crisis in Lebanon, leading to the collapse in January of the country’s Western-backed unity government.

The indictment comes at a delicate time for Hezbollah, as its ally Syrian President Bashar Assad faces an unprecedented domestic uprising against his rule.

The Hariri murder sparked a wave of massive protests in Lebanon in 2005 which, combined with international pressure, forced Syria to withdraw its troops from the country, ending a 29-year deployment.