WASHINGTON (Reuters) - The United States on Monday labeled former Lebanese government minister Michel Samaha, an ally of Syrian President Bashar al-Assad, a terrorist and froze his assets, saying he had supported attempts by Damascus to incite violence in Lebanon.

The U.S. Treasury Department designated Samaha, a former minister of information and tourism now in custody in Lebanon, a "global terrorist" and said he had collaborated with the Assad government to destabilize Lebanon.

"The United States will continue to expose any attempts by the (Assad) regime to meddle in the affairs of its neighbors and further destabilize the region," the Treasury Department said in a statement.

The department said its designation, which freezes any assets held by Samaha under U.S. jurisdiction, also prohibits Americans from doing business with Samaha.

The State Department, in a parallel announcement, noted that Samaha had been charged in Lebanon with working with a top Syrian security official to plot the assassination of political and religious figures in Lebanon through targeted bombings in July.

"The goal of these attacks appears to have been an attempt to incite sectarian clashes in Lebanon on behalf of the Syrian regime," the State Department said, adding that Samaha had also been accused of transporting explosives for the planned attacks into Lebanon.

Samaha was arrested by Lebanese authorities in August for allegedly plotting to incite violence in Lebanon. He has been an outspoken supporter of Assad during the 17-month-old Syrian uprising.

He served as a minister in three Lebanese governments between 1992 and 2004, when Syria dominated politics and security in its smaller neighbor. Samaha is also a former member of parliament.

In 2007, Samaha was named on a White House-issued list of Lebanese and Syrian figures suspected of working to undermine Lebanon's stability and the Western-backed Beirut government in office at the time.

Lebanon has indicted two Syrians including General Ali Mamlouk, a top security official, in connection with the case, marking a major break with the past when such action against Damascus or its Lebanese allies would have been unthinkable.

The case, which has not yet gone to trial, evokes political violence dating back decades in Lebanon, including the 1977 assassination of Druze leader Kamal Jumblatt and the 2005 killing of Sunni politician Rafik al-Hariri, among a long list of others. If proven true, it would be a blow to Hezbollah, Syria's powerful, Iranian-backed Shi'ite ally.

Syria's opponents in Lebanon, some of them survivors of assassination attempts, have leaped on the case as proof of the nefarious role played by Damascus in a country that has been an arena for power struggles among foreign governments including the United States, Israel, Iran and Saudi Arabia.

(Reporting by Jason Lange and Andrew Quinn; Editing by David Storey and Eric Beech)