Bush reaffirmed Washington's support for Prime Minister Fuad Siniora amid deadly violence pitting mainly Sunni supporters of the government and militants loyal to the Shiite Hezbollah-led opposition.
"I strongly condemn Hezbollah's recent efforts, and those of their foreign sponsors in Tehran and Damascus, to use violence and intimidation to bend the government and people of Lebanon to their will," Bush said in a statement.
"The international community will not allow the Iranian and Syrian regimes, via their proxies, to return Lebanon to foreign domination and control," he said.
Bush said Washington would help Siniora by strengthening his armed forces.
"It's probably the most practical way that we can get some help to him quickly," he told Al Arabiya television, according to a transcript of the interview.
"They're not great yet, but they're pretty good. And we want to make them better so that they can respond."
Bush said he planned to consult with regional leaders durings his trip to the Middle East this week in order to coordinate efforts to support Siniora's government and implement UN resolutions supporting Lebanon's sovereignty.
"It is critical that the international community come together to assist the Lebanese people in their hour of need," said the US leader, who leaves Tuesday on a five-day trip to Israel, Saudi Arabia and Egypt.
"The Lebanese people have sacrificed much for the sake of their freedom, and the United States will continue to stand with them against this latest assault on their independence and security," he said in the statement.
The northern Lebanese city of Tripoli was rocked by fierce fighting for a second day on Tuesday, exacerbating tensions after days of deadly sectarian battles that have driven the nation to the brink of full-blown civil war.
At least one man was killed in clashes on Monday between supporters of the Western-backed government and militants loyal to the Shiite Hezbollah-led opposition in the port city, a security official said.
Six days of fighting have left at least 61 people dead and nearly 200 wounded, the worst unrest since the 1975-1990 civil war.
Lebanon's political standoff, which erupted in November 2006 when six pro-Syrian ministers quit, has left the country without a president since last November when Damascus protege Emile Lahoud's term ended.
In a statement issued at the United Nations, a group of Western and Arab nations, dubbed Friends of Lebanon, called for an immediate end to the fighting and the quick election of a president "without prior conditions."
The Friends of Lebanon groups 12 Western and Arab countries — the United States, France, Britain, Italy, Germany, Spain, Saudi Arabia, the United Arab Emirates, Egypt, Jordan, Kuwait and Qatar — as well as the heads of the UN, Arab League and the Council of European Union.
Foreign ministers and officials from the group held a conference call on Monday along with an unidentified Lebanese minister.
At the UN, US Ambassador UN Zalmay Khalilzad called for the UN Security Council to hold formal discussions on Lebanon as soon as possible.
"We believe there should be action in the Security Council on the situation in Lebanon," Khalilzad told reporters.
