Secretary of State Condoleezza Rice reaffirmed U.S. support for Lebanon's sovereignty and democracy in a surprise visit Thursday and called on Syria to cooperate with a U.N. investigation into the assassination of former Premier Rafik Hariri.

Speaking after a meeting with Prime Minister Fuad Saniora, Rice also said Iran must live up to its international obligation and not seek nuclear weapons.

Her visit to Lebanon came amid sharpening domestic political tensions over attempts to remove pro-Syrian President Emile Lahoud by the anti-Syrian parliamentary majority.

"It's up to the Lebanese to decide who is going to govern this country," she said.

She reiterated support for the Saniora government as it continues the process of political reform and separation from Syria, which controlled Lebanon for almost three decades and withdrew its army in April.

Rice said "there must be full cooperation" by Syria with the U.N. investigation into the Hariri assassination. The U.N. probe has accused Syria of failing to cooperate fully with the probe, which has already implicated Syrian officials in the assassination.

Rice will not meet Lahoud on her visit, and took no specific position on whether he should stay or go.

She told reporters accompanying her that the Lebanese "need a presidency that looks forward, not back, and that defends Lebanese sovereignty."

Asked if Lahoud is an obstacle to that progress, Rice replied, "The Lebanese people will have to decide what the obstacles to their progress are, but I think they do want to look forward."

Rice's visit was timed close to the anniversary this month of the 2005 assassination of Rafik Hariri, a Lebanese politician who had tried to pry his country from 30 years of Syrian political domination.

Hariri's death launched street protests that eventually forced Syrian troops from Lebanon last spring, but the United States claims that Syrian intelligence agents remain and that Damascus is still trying to meddle in Lebanese politics.

Rice met with Lahoud on her first visit to Lebanon as secretary of state last year, but made clear the visit was merely a pro forma nicety. Her first stops on that trip were the Hariri family compound and his burial shrine.

Buoyed by street protests marking the Hariri anniversary, the anti-Syrian coalition launched a campaign against Lahoud that could include strikes and street protests, and possibly a march on the presidential palace.

There are warnings of counter-demonstrations, which could lead to clashes. Lahoud on Monday warned that "security is a red line," implicitly hinting at the use of force.

Lahoud, Damascus' top ally in Beirut, was elected by Parliament before the Syrian pullout. His term runs through 2007 and he has pledged to remain until the last moment.

Lahoud won a three-year extension of his term in 2004 under what was widely seen as Syrian pressure, and anti-Syrian groups are looking to reverse that.

The anti-Syrian coalition says Lahoud is politically isolated at home and diplomatically isolated abroad. A U.S.-backed 2004 U.N. Security Council resolution called for new presidential elections.

Anti-Syrian groups say Lahoud serves Syria's interests, implicitly blaming him for a series of bombings and assassinations that killed three anti-Syrian figures, an accusation Lahoud rejects. Four generals, including the commander of Lahoud's Presidential Guards and two of his intelligence aides, are charged with involvement in Hariri's murder.

"The issue of the presidency should be done with," Samir Geagea, one of the anti-Syrian leaders, told reporters Sunday. "It must be rescued from its current state."

Anti-Syrian lawmakers have a slim majority in the parliament, but they don't have the necessary two-thirds hold on the legislature to oust Lahoud by their self-imposed deadline of March 14.

The anti-Syrian coalition plans two petitions in coming days that do not require a two-thirds majority: one stating that lawmakers were threatened by Syria to vote for the extension, and another declaring the presidential post is vacant because the extension was illegal. The coalition would then elect a new leader.

To prevail, the anti-Syrian coalition will have to win over other factions. It also must have the consent of Cardinal Nasrallah Sfeir, the influential head of the Maronite Catholic Church with whom Rice met.

She described him afterward as a strong voice calling for freedom and democracy.

Lahoud is a Maronite, as all presidents have to be under the sectarian system of power sharing, and the views of the church's patriarch on the campaign to remove the president would be significant.

In brief remarks to reporters after the meeting at Bkirki in the mountains northeast of Beirut, Rice stressed the United States would continue to support Lebanon and said Washington looked forward to the day when the country was free of threats and lived in peace.

Sfeir, fearful of violence and a power vacuum that could threaten the Maronites' hold on the post, has cautioned against removing the president through street protests and before an agreement is reached on a replacement.

"This alignment of one group against the other, as if an expected war is awaiting to be waged ... does not bode well," the widely respected patriarch said in a Sunday sermon. "It heralds imminent evil."