The Foreign Office today warned travellers to Kenya, Ethiopia and Djibouti that they faced an increased and significant threat from terrorism.
However, it stopped short of advising against non-essential travel to the region.
"All visitors to these countries should take sensible precautions and maintain a high level of vigilance in public places," said a Foreign Office spokesperson. "The threat posed by terrorism is significant."
The Foreign Office said that it was continuing to receive reports that Britons were at risk of terrorist attacks on areas frequented by westerners. It added that the terrorist threat in East Africa was "continuing" and that terrorist groups had the "intention", as well as the capacity, to carry out attacks.
The Foreign Office toughened its advice on Kenya. It said: "All UK nationals in Kenya should be vigilant, particularly in public places frequented by foreigners such as hotels, restaurants, nightclubs and shopping malls. In particular there is a potential threat against Western interests in Nairobi."
Travel to Ethiopia was described as high risk due to the dangers of terrorism throughout the country. Certain parts of the country are off limits to Britons and UK nationals should only enter other regions for essential reasons.
Djibouti was described as risky, mainly because of the large US military presence which "may increase the likelihood of terrorist attacks against Western interests."
On November 28 last year, 11 Kenyans and three Israeli tourists died when terrorists bombed a hotel near the coastal resort of Mombasa in southern Kenya.
On the same day, unidentified assailants fired two missiles that narrowly missed a charter airliner as it took off from Mombasa airport with Israeli tourists returning to Tel Aviv. Both attacks were later claimed by al-Qaida.
Last December the British high commission in Nairobi was closed for four days following a specific threat.
There was a terrorist attack on the US embassy in Nairobi in August 1998 in which 232 people were killed.
· Full details of the revised Foreign Office travel advice can be found at www.fco.gov.uk/travel.
