Hezbollah's Shiite supporters attacked a top U.S. diplomat's motorcade with stones in southern Lebanon on Wednesday, protesting her first visit to the militant group's stronghold, witnesses said.

Security officials and witnesses said no one was hurt in the attack, but at least one of the U.S. convoy's 10 bulletproof vehicles was hit and broke down.

The attack occurred Wednesday afternoon after U.S. Charge d'Affaires Michele Sison inspected some social and educational projects financed by the U.S. government in the southern market town of Nabatiyeh, a Hezbollah stronghold.

Sison was having lunch at the residence of Abdullah Bitar, the head of Nabatiyeh's business organization, when about 100 Hezbollah supporters gathered outside the house and began shouting anti-U.S. slogans, witnesses said.

"Death to America!" the protesters shouted.

Sison and the accompanying delegation interrupted their lunch and left the town, witnesses said.

U.S. officials were not immediately available to comment on the incident.

A Lebanese security official said the back shield of one of the convoy's vehicles sustained cracks after it was hit with stones. The vehicle broke down and had to be towed to a police barracks in Nabatiyeh, the official said.

He and other security officials spoke on condition of anonymity because they were not authorized to talk to media, and witnesses also requested anonymity out of security concerns.

A Hezbollah official in Beirut refused to comment, saying he had no knowledge of the incident.

It was Sison's first visit to southern Lebanon since she arrived in the country in January.

The attack came two days after U.S. Secretary of State Condoleezza Rice visited Beirut, putting an American stamp of approval on plans for a new government in Lebanon that would increase the power of Hezbollah militants.

The U.S. regards the Iranian- and Syrian-backed Hezbollah as a terrorist group and has no dealings with it.

Though rare now, attacks on U.S. diplomats and interests in Lebanon were once common. Washington blames Hezbollah for the bombing deaths of 241 U.S. Marines at their Beirut barracks in 1983, as well as for two attacks on the U.S. Embassy in Beirut and the 1985 TWA hijacking that killed an American serviceman on board.

Hezbollah denies the accusations and says it now opposes terrorism.

The first such attack in Lebanon in more than two decades was a car bomb that targeted a U.S. Embassy vehicle north of Beirut in January, killing three passers-by and wounding 26 others.

Hezbollah, which is both an armed group and a political party, gained veto power over the Western-backed government in an agreement last month that ended an 18-month political stalemate. The deal followed bloody sectarian street clashes between Hezbollah's Shiite supporters and pro-government Sunni loyalists that left 81 people dead.