The United States warned its nationals Saturday of "potential for retaliation'' after two key Al-Qaeda figures were killed in an air raid in Yemen.
The State department issued a global travel alert to US citizens, a day after Washington confirmed that US-Yemeni citizen Anwar al-Awlaqi, the external operations leader of Al-Qaeda in the Arabian Peninsula (AQAP), was killed.
"Awlaqi's standing as a preeminent English-language advocate of violence could potentially trigger anti-American acts worldwide to avenge his death,'' the State Department said in its alert.
"In the past Awlaqi and other members of AQAP have called for attacks against the United States, US citizens and US interests,'' it added.
Yemen's defense ministry said Awlaqi, an Al-Qaeda leader, was killed Friday morning, while a man wounded in the attack was quoted as saying seven people were killed in the air strike in Marib province, a hotbed of Al-Qaeda activity.
The ministry said among those killed was Pakistani-American Samir Khan.
New York City police commissioner Ray Kelly has described Khan as the publisher of Al-Qaeda's English-language magazine "Inspire.''
Kelly said Friday that his force was on alert following the killing in Yemen of Awlaqi, acknowledging the US-born Islamic cleric's sympathizers might seek revenge.
"We know al-Awlaqi had followers in the United States, including New York City, and for that reason we remain alert to the possibility that someone might want to avenge his death,'' Kelly said in a statement.
More than 2,750 people were killed when the World Trade Center in New York was destroyed in the September 11, 2001 attacks.