WASHINGTON, Jan 29 (Reuters) - President George W. Bush accused Iran, Syria and Hezbollah on Monday of fomenting the latest violence in Lebanon in a bid to topple its government and said "those responsible for creating chaos must be called to account." Bush's comments were his first on last week's sectarian clashes in Beirut between pro- and anti-government activists that left four people dead and and 200 injured, rekindling memories of Lebanon's 1975-1990 civil war. "I am deeply disappointed by the recent violence and bloodshed on the streets of Lebanon," Bush said in a written statement. Bush reiterated a U.S. accusation that Tehran, Damascus and Hezbollah, a Lebanese guerrilla group backed by both countries, were trying to bring down the elected government of Prime Minister Fouad Siniora. Washington, bogged down in an unpopular war in Iraq, has held up Lebanon as an example of an emerging democracy in the Middle East. "Those responsible for creating chaos (in Lebanon) must be called to account," Bush said. "Syria, Iran and Hezbollah are working to destabilize Lebanese society," he added. "Their goals are clear." "They foment violence in order to prevent the establishment of a special tribunal in response to former Prime Minister Hariri's assassination, to prevent full implementation of U.N. Security Council resolutions calling for Hezbollah's disarmament and to bring down Lebanon's democratically elected government," he said. Iran and Syria have denied such accusations. Tehran was also the target of Bush's warning earlier on Monday that the United States would respond firmly if Iran fuels the violence in Iraq. Iran is facing a U.S.-led diplomatic offensive against its nuclear program. Bush pledged continued support for Lebanon, saying he would ask Congress for $770 million in aid that Washington promised last week as part of a $7.62 billion international package hammered out at a donors' conference in Paris.