(Adds details, background) BEIRUT, March 6 (Reuters) - The U.S. embassy in Lebanon has urged its citizens residing there to keep a low profile, citing concern that "extremist groups" may be planning attacks against Americans. "There is a general concern that extremist groups may be planning to attack U.S. citizens and interests in Lebanon," the embassy said in a statement dated March 4, posted on its Web site and circulated to U.S. citizens. The United States backs the anti-Syrian governing coalition which is locked in a 16-month-old power struggle with an opposition led by Hezbollah -- a faction supported by Syria and Iran and which Washington lists as a terrorist group. Tension has increased since the United States last week deployed three warships in the eastern Mediterranean off the coast of Lebanon to send a signal to Syria, which Washington accuses of meddling in the country. "The U.S. Embassy urges U.S. citizens who live, work or are travelling in Lebanon to exercise responsible security practices," the statement said, adding that Americans should "avoid predictable or habitual behavior". Both Hezbollah and Syria criticised the deployment of the warships, saying it would endanger regional stability and prolong Lebanon's crisis. The political standoff, punctuated by assassinations, bombings and sectarian violence, has left Lebanon without a president since November and paralysed much of government. In January, a bomb damaged a U.S. diplomatic car and killed three people in a Christian suburb north of Beirut. The embassy restricted its staff movements after the blast. The assassination of Hezbollah military commander Imad Moughniyah in Damascus last month has added to tensions. Hezbollah said Israel was behind his killing, which Washington welcomed. Israel has denied involvement, but Moughniyah had been sought by its Mossad spy service for two decades and was also on the United States' most wanted list. Saudi Arabia, a staunch supporter of the Sunni-led ruling coalition, advised its citizens this month to leave Lebanon immediately due to the security situation. Many countries have advised their nationals against non-essential travel to Lebanon. (Writing by Yara Bayoumy, editing by Mark Trevelyan)
A protester carries a portrait of the late Ayatollah Ruhollah Khomeini (L) and Iran's supreme leader, Ayatollah Ali Khamenei, during a rally in support of Iran's nuclear program, in front of ...
