BEIRUT (Reuters) - A Lebanese Christian political leader and ally of the Shi'ite group Hezbollah said he escaped an assassination attempt when his convoy came under fire in southern Lebanon.

Michel Aoun, head of the Free Patriotic Movement (FPM), was returning to Beirut on Saturday evening when one of the cars in his convoy was shot at in the mainly Sunni city of Sidon, a statement on the FPM website said.

"I have been exposed to three assassination attempts (in the past) and the perpetrators were discovered," the website quoted Aoun as saying. "This is the fourth and we hope they will be revealed."

The attack on Aoun's convoy is the latest reported threat to prominent politicians in Lebanon, where tensions over the uprising in neighboring Syria against President Bashar al-Assad have polarized chronic sectarian and political rifts.

Two other Christian politicians, Samir Geagea and Boutros Harb, have said they were targets earlier this year. Geagea said shots were fired at his home in northern Lebanon in April and Harb said security forces found a bomb in the lift of his office building in July.

Aoun's largely Christian FPM is allied with pro-Assad Hezbollah in the government of Prime Minister Najib Mikati, while Geagea and Harb are both staunchly anti-Assad.

Other politicians including Shi'ite parliamentary speaker Nabih Berri and Druze leader Walid Jumblatt have been warned about threats against them, political sources have said.

Former prime minister Saad al-Hariri, whose father was assassinated in a February 2005 Beirut bombing, has been living outside Lebanon for nearly a year and a half, partly due to fears for his security.

(Reporting by Dominic Evans; Editing by Janet Lawrence)