Britain and the US are to combine forces to tackle the threat of terrorism emanating from Yemen and Somalia.

Downing Street said both the US and UK would fund a counter-terrorism police unit in Yemen.The two countries will also push for more UN intervention to tackle radical Islamic groups in Somalia.

The announcement came after the Prime Minister called a summit of world leaders in London later this month to discuss Yemen.The US and UK have been moved to act following the failed Detroit airliner plot.

Umar Farouk Abdul Mutallab, the 23-year-old Nigerian who allegedly attempted to detonate a bomb on an aeroplane approaching Detroit on Christmas Day, is believed to have become radicalised during a visit to Yemen and trained there within the last six months.President Obama said Mutallab had been trained by Al-Qaeda .

A Number 10 spokeswoman said Gordon Brown and Mr Obama had spoken several times on the telephone since the failed attack, and decided to increase UK-US co-operation.Mr Brown announced last week a review of airport security.Options being looked at include full body scanners.

The results of the review will be delivered "in days" and Mr Brown will hold talks with ministerial colleagues and intelligence advisors this week.