British officials say terrorists could still be planning to carry out attacks on the country, although authorities believe they have detained the main suspects in a plot to blow up U.S.-bound flights.

Home Secretary John Reid told British television (BBC) Sunday the threat of a terrorist attack in Britain is still very substantial.

He says at least four major terrorist plots have been thwarted since the deadly July seventh attacks on the London transit system last year.

Twenty-three people are in detention in London, suspected of planning to detonate liquid explosives aboard as many as 10 airliners.  London investigators say they arrested the suspects Thursday after a conspirator in Pakistan urged an accomplice in Britain to quickly carry out the plan.

Pakistani officials also have arrested several suspects, including a Briton (Rashid Rauf) allegedly tied to al-Qaida in Afghanistan.

British investigators are searching for possible links to last July's suicide bombings, which killed 52 people and wounded hundreds more.

Authorities in the United States say they are also looking for possible U.S. ties to the conspiracy. 

Some infomation for this report was provided by AFAP, AP and Reuters.