(refiles adding byline) (Adds Arab League mediation, Syrian comment)

By Yara Bayoumy

BEIRUT, Jan 16 (Reuters) - The U.S. embassy in Lebanon has restricted its staff movements and urged Americans to avoid popular areas, a day after a bomb damaged a U.S. diplomatic car and killed three people in a Christian suburb north of Beirut.

The bomb blast coincided with President George W. Bush's week-long tour to the Middle East and political conflict in Lebanon between the U.S.-backed governing coalition and the Damascus-backed opposition.

"The Embassy ... reminds all Americans residing in Lebanon to maintain a high level of vigilance, especially when planning travel," the U.S. Embassy in Lebanon said on its Web site in a statement dated on Tuesday.

"Americans are also advised to avoid popular gathering spots and to report any suspicious activity to local law enforcement officials," it said, adding limits had been imposed on embassy personnel's movements.

The attack, a 20-minute drive from the heavily fortified U.S. embassy, revived memories of attacks on U.S. personnel in Lebanon during the 1975-1990 civil war.

On Wednesday, the U.S. State Department said it appeared the U.S. embassy car had been the intended target of the attack.

State Department spokesman Sean McCormack said the United States did not know who was responsible but "preliminary evidence would indicate that it (the car) was targeted".

A joint diplomatic and security team, including the FBI, was travelling to the area on Wednesday to investigate, he added.

In Beirut, security sources said investigators were draining water from a blast crater to find remnants of Tuesday's bomb, which also wounded 16 people, including an embassy driver.

Lebanese internal security forces said the explosion had been caused by about 20 kg (44 lb) of TNT explosives placed in a Honda car.

The United States is the anti-Syrian majority's most influential backer in its political battle with the Hezbollah-led opposition.

The conflict has paralysed Prime Minister Fouad Siniora's government for more than a year and blocked the election of army chief General Michel Suleiman as president, leaving Lebanon with no head of state for the first time since the civil war.

Arab League chief Amr Moussa resumed mediation between rival Lebanese leaders on Wednesday to push them towards agreement on an Arab initiative to end the crisis.

Separately, Syria said on Wednesday it could not force its Lebanese allies to accept a solution to the political crisis.

"Asking Syria to pressure its allies in Lebanon is anathema to the Arab initiative, which activated a joint Arab responsibility to reach a settlement," Information Minister Mohsen Bilal told reporters. His remarks were in response to Saudi criticism to Syria's role in Lebanon. (Writing by Yara Bayoumy; Editing by Caroline Drees)

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