WASHINGTON -?The United States on Saturday warned its citizens of potential retaliatory attacks worldwide following the killings of two senior al-Qaida members in a US air raid in Yemen a day earlier.

"The death of Awlaki, in the near term, could provide motivation for anti-American attacks worldwide from individuals or groups seeking to retaliate against US citizens or interests because of this action," the State Department said in a worldwide travel alert.

US and Yemeni government officials confirmed on Friday that dual US-Yemeni citizen Anwar al-Awlaki, the external operations leader of al-Qaida in the Arabian Peninsula (AQAP), and Samir Khan, a US citizen of Pakistani descent who was co-editor of al-Qaida' s English-language magazine "Inspire," were both killed in US drone attacks in northeastern Yemen in the early morning.

"In the past, Awlaki and other members of AQAP have called for attacks against the United States, US citizens and US interests," the State Department said. "Awlaqi's standing as a preeminent English-language advocate of violence could potentially trigger anti-American acts worldwide to avenge his death."

US President Barack Obama said on Friday that the killing of al-Awlaki is a major blow to AQAP, which has tried to bomb US targets.