The Bush administration is accusing Syria, Iran and the Hezbollah militants they back of trying to overthrow the Lebanese government. Officials acknowledged the United States can do little to prevent outside interference with Beirut's fragile democracy.

White House spokesman Tony Snow cited "mounting evidence that the Syrian and Iranian governments, Hezbollah and their Lebanese allies are preparing plans to topple Lebanon's democratically elected government."

A strongly worded statement from the White House did not detail the evidence. It singled out Syria for an alleged plan to derail possible prosecutions for the assassination of Rafik Hariri, a Lebanese politician who had tried to draw his country away from Syrian domination.

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The U.S. ambassador to the United Nations, John Bolton, accused Syria and Iran on Monday of violating a U.N. embargo meant to keep Hezbollah from rearming after the 34-day war it waged with Israel last summer.

Bolton said late Wednesday he thinks the continued violations of U.N. resolution 1559, which demanded disarmament of all militias in Lebanon, and U.N. resolution 1701, which ended the summer war, are part of the "evidence base" the White House used for its statement.

"And it's one of the reasons why we want to accelerate our support for the democratic government of Lebanon," Bolton told reporters.

Syria denies it is violating the embargo. It and Iran provide weaponry, training and money to Hezbollah, an Islamic militant group that held de facto control in southern Lebanon before the cross-border war.

Hezbollah leader Sheik Hassan Nasrallah gave the government of Prime Minister Fuad Saniora an ultimatum on Tuesday: establish a cabinet of "national unity" by Nov. 13 or face street protests. Such a cabinet would give the Islamic militants and their allies veto power over key decisions.

U.S. officials said they consider Nasrallah's threat serious, especially if supporters of the embattled Saniora should take to the streets in protests that Saniora might be unable to control. The United States considers Hezbollah a terrorist group and refuses to deal directly with it.

Saniora is a lukewarm U.S. ally who has maintained control in part by distributing favors and political power among Lebanon's competing political and religious factions and by appealing to some of the same nationalist sentiment that sustains Hezbollah.

The U.S. initially resisted international pressure for a cease-fire when Hezbollah provoked the fighting with Israel but moved for a U.N.-mandated end to the war, partly out of fear that Saniora's government could fall. Saniora emerged from the war with improved credentials as a statesman but without significantly greater political strength.

"Ultimately, what we can do is try to, as best we can, support Prime Minister Saniora politically, diplomatically, economically," State Department spokesman Sean McCormack said. "This is the elected government of Lebanon. All that said, we're not going to interfere in Lebanon's domestic politics."

Since fighting ended Aug. 14, tensions have increased between Hezbollah and its pro-Syrian allies, and the Lebanese government's anti-Syrian majority.

"What we don't want to see is others interfering in Lebanon's domestic politics," McCormack said. "And I'm afraid that that is our fear."

Syria was the dominant political and military power in Lebanon for nearly three decades before it pulled its forces from the country last year. The United States has claimed that Syrian intelligence agents remain and hold considerable sway; Syria denies it.

France's U.N. Ambassador, Jean-Marc de La Sabliere, asked whether his government had similar evidence, said: "There are here and there rumors that some people who are not maybe satisfied with having (resolutions) 1559 or 1701 well-implemented are trying to make difficulties."

"I hope it's not true, but what I can tell you is that ... the international community is supporting prime minister Siniora, and the international community will do its best to have Resol 1701 implemented," de La Sabliere said.

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