The United States says extremists from Somalia may be planning suicide attacks in Kenya and Ethiopia.

The U.S. embassy in Nairobi issued the warning Thursday, telling Americans in those countries to remain vigilant. It said it has received terrorist threats that specifically mention the possibility of suicide bombings at prominent landmarks in Kenya and Ethiopia.

U.S. officials have not identified the extremists behind the purported threats. However, a State Department spokesman who was asked about the warning Thursday noted that the U.S. is concerned about terrorists in Somalia with links to outside terrorist groups.

The United States has repeatedly expressed concern that Somalia's powerful Islamist movement may have links to al-Qaida.

This new warning comes amid rising concern about all-out war between the Islamists and Somalia's weak interim government.

Both Kenya and Ethiopia back a proposed deployment of peacekeepers to Somalia to support the government.

The Islamists vehemently oppose that idea, and they recently declared a holy war on Ethiopia for sending its own troops onto Somali soil to give the government protection.