JERUSALEM - US President George W. Bush on Monday called Iran the "single biggest threat" to peace in the Middle East ahead of a visit to the region centered on celebrations of Israel's 60th anniversary.

"To me it's the single biggest threat to peace in the Middle East, the Iranian regime," because of its nuclear programme and its support of groups like the Lebanese Hezbollah militia, Bush told Israel's Channel 10.

"Their funding of Hezbollah -- look what's happening in Lebanon now, a young democracy trying to survive," Bush said in excerpts of an interview to be broadcast in its entirety on Tuesday.

In recent days Lebanon has been driven to the brink of civil war after days of deadly sectarian street clashes between the Shiite Hezbollah and its allies and Sunni Muslim supporters of the US-backed government.

"By the way it's in Israel's interest that the Lebanese democracy survives. You need to be concerned about Iran and you are concerned about Iran and so are we," Bush said.

The US and Israel accuse Iran of pursuing nuclear weapons and Israel has considered the Islamic republic its greatest strategic threat in the wake of repeated statements by its president predicting the Jewish state's demise.

Iran insists its nuclear programme is entirely peaceful.

Bush was due to meet Israeli Prime Minister Ehud Olmert on Wednesday at the start of a five-day trip anchored on Israel's 60th anniversary celebrations and aimed at bolstering US-backed Middle East peace talks launched in November.

Bush declined to comment on a major corruption investigation recently launched against the beleaguered Israeli premier, saying only that he has "great relations with the prime minister."

"I find him to be a frank man and an honest man and an open man," Bush said.

Olmert is suspected of having received funds illegally from a US businessman before he became premier in 2006.