The Associated Press
In this photo taken late Thursday, May 15, 2014, British tourists queue to prepare to leave the international airport in Mombasa, Kenya. A number of British tourists left the country by charter flight Thursday following a new travel advisory from the British Foreign and Commonwealth Office (FCO) advising against all but essential travel to Mombasa island. (AP Photo)

NAIROBI, Kenya — Marines at the U.S. Embassy in Nairobi patrol the grounds in bullet proof vests amid an increase in the frequency of emergency drills.

The U.S. Embassy on Friday sent out a new travel alert warning of a continued terrorist threat in a country where the embassy suffered a devastating attack in 1998.

An earlier warning this week said for the first time that the embassy itself is taking new steps to increase security "due to recent threat information regarding the international community."

Britain's government also warned its citizens this week to avoid the coastal city of Mombasa and beach towns nearby, prompting a travel company to send home hundreds of British citizens from their beach vacations.

Security concerns have long been high in Kenya because of its proximity to Somalia.