The Foreign Office has issued warnings to British people planning to travel to parts of the Middle East because of the threat of terrorism.

They have been advised to avoid Yemen except on essential business, and to be vigilant in Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates.

The warnings come amid the tightening of measures to tackle the threat of terrorism, and a day after the Home Office issued an alert in error.

It spoke of the danger of terrorist attacks including "dirty" nuclear bombs in the UK.

Retaliation

There have been a number of terrorist attacks in Yemen over recent years.

There have also been rumours that some al-Qaeda members have made the Middle Eastern state their base since the overthrow of the Taleban in Afghanistan.

The Foreign Office warned that there may be a retaliation against Western outlets in Yemen following the killing last week of six suspected al-Qaeda members, including Osama Bin Laden's top lieutenant in the country, Qaed Salim Sinan al-Harethi.

There have been attacks on foreign targets in Yemen in recent years - including a bomb attack on the British Embassy in 2000.

Alert

In 1998, a group of tourists were kidnapped and held hostage by a little-known Islamist group in the Abyan region of Yemen.

Four of them, including three Britons, were killed in a shoot-out when local government forces staged a rescue attempt.

In the Gulf states mentioned, Britons are asked to be particularly alert in places frequented by foreigners, such as hotels, restaurants and shopping malls.

British citizens have also been warned against travel to some areas of South East Asia - Indonesia being one of them, following last month's bomb blast in Bali.