BEIRUT: A new political crisis looms in Lebanon as pressure mounts on Prime Minister Najib Mikati to deliver on his pledge to cooperate with a UN-backed court probing the murder of ex-premier Rafiq Hariri.

"On the one hand, Mikati is under massive pressure by the international community to fund the court," said Imad Salamey, political science professor at the Lebanese American University.

"On the other, if he stands up to Hezbollah and comes out in support of the Special Tribunal for Lebanon (STL), his political career is over."

The powerful militant group dominates Mikati's government and has waged a relentless campaign against the STL, which has charged four Hezbollah operatives in Hariri's 2005 assassination.

Hassan Nasrallah, head of the Syrian- and Iranian-backed Shiite group, on Monday reiterated his opposition to Lebanon paying its annual share to the Netherlands-based tribunal that for 2011 amounts to about $35 million (25.2 million euros) -- or 49 percent of the court's budget.

But the international community is clearly growing impatient with Mikati, with the United States this week bluntly warning of "serious consequences" should his government fail to pay up.

"We are probably headed for a tug-of-war over the financing of the tribunal, and hence for more political tensions," said Paul Salem, head of the Beirut-based Carnegie Middle East Center.

"Refusing to fund the tribunal will pit Lebanon against the international community and raise the risk of sanctions," Salem told AFP.

Lebanon in previous years has contributed its share to the STL, under the Western-backed government of then-premier Saad Hariri, son of the slain leader, and his predecessor.

In recent weeks, however, Mikati has received a series of notifications from the court on the overdue funds.

The Forbes-listed Sunni tycoon, who was ushered in as premier after Hezbollah toppled Saad Hariri's cabinet in a feud over the STL, has from the onset stated his commitment to international resolutions, including the tribunal.

But the opposition, led by Hariri, has slammed Mikati for failing to act, accusing him of being a Hezbollah puppet and buying time.

"That fact that Mikati is choosing to take as much time as possible with the financing ... may well be a means of hiding behind a bigger debate over the tribunal," said Mohamad Chatah, a senior advisor to Hariri.

Founded under Chapter 7 of the UN Charter, the STL is the first international court with jurisdiction to try an act of terrorism.

The tribunal's mandate expires in March and it is widely expected that Hezbollah will demand the Lebanese government end all ties with the STL.

Experts warn such a scenario could alienate Lebanon from the international community.

"Should the Lebanese government decide to end its agreement with the court, the United Nations could consider the country as impeding justice," said attorney Mohamed Matar, an expert on the STL.

"In that case, the United Nations could take action against the government, ranging from a formal demand that Lebanon comply with the STL to the imposition of sanctions."

But some experts say Hezbollah will try to wriggle its way out of the gathering storm, especially as its ally, Syrian President Bashar al-Assad, battles an unprecedented revolt threatening to topple his regime.

"It is in Hezbollah's interests to ensure this regionally- and internationally-accepted government does not collapse, especially as it knows that none of the party's (indicted) members will ever be arrested," said Salem.

"But if the government fails to find a solution, then Mikati could end up resigning."

Salamey added that working in Mikati's favour, at least for now, is the need of Western countries for stability in Lebanon.

"Mikati is probably counting on international pressure waning as crises in other countries emerge, especially Syria," the university professor said.