Britain and the US are to join forces to tackle the "evolving threat" from Islamist groups in Yemen and Somalia, Downing Street has announced.

英国政府宣布，英国将与美国联合处理也门和索马里的伊斯兰教团体对其“带来的威胁”。

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The leaders have agreed to intensify US-UK work in Yemen and Somalia

Officials said the UK and the US would jointly² fund a counter-terrorism police unit in Yemen in the wake of紧紧跟随 an alleged³ bomb airline attack over Detroit.

Barack Obama has sent his top Middle East general to meet Yemen's president.

The US president has alleged that the Christmas Day bomb suspect was trained by a Yemen-based al-Qaeda offshoot.

Gen David Petraeus - who is responsible for US Middle East and Central Asian operations - reportedly said the US was keen to support Yemen's fight against al-Qaeda.

On Saturday, Mr Obama for the first time publicly accused an offshoot of al-Qaeda, based in Yemen, over the alleged attempt by Nigerian Umar Farouk Abdulmutallab to blow up an airliner⁴ over Detroit.

'Terror incubator'

A statement from No 10 said Downing Street and White House officials had discussed "increased UK-US working" in a series of phone calls since the alleged failed plot on Christmas Day.

Mr Brown has called Yemen "both an incubator孵卵器，保温箱 and potential safe haven⁵安全港 for terrorism" and said it presented "a regional and global threat".

The UK is one of Yemen's leading donors⁶ and is already helping⁷ to train counter-terrorism officials in the country.

The increased assistance from both the UK and US will include support for the Yemeni coastguard operation.

Downing Street told the BBC: "This is a decision reached after discussion with the Yemeni government and the White House.

"The details are still to be worked out but this will build on the work already being done by the UK to help the Yemeni government combat terrorism."

Downing Street also confirmed Mr Brown and Mr Obama will push at the UN security council for a larger peacekeeping force in Somalia.

Gen David Petraeus flew to Yemen to discuss stepping up co-operation between the two countries in the fight against al- Qaeda, according to the Yemeni state news agency.

It says Gen Petraeus met President Ali Abdallah Saleh in the capital Sana'a and handed over a letter from President Obama.

The BBC's world affairs correspondent Caroline Hawley said there had been growing concern for some time about al-Qaeda exploiting Yemen's troubles to establish a safe haven in the country's ungoverned spaces.

"But the failed bomb attack last week has put the international spotlight⁸ on the Arab world's poorest country," she added.

On Tuesday, Yemen's Foreign Minister Abu Bakr al-Qirbi told the BBC that Yemen had the will and ability to deal with al-Qaeda, but needed more support from the West.

"We need more training," he said.

"We have to expand our counter-terrorism units and this means providing them with the necessary training, military equipment, ways of transportation - we are very short of helicopters."

In Somalia, the prime minister and president believe a larger UN peacekeeping force is required.

Somalia has not had a functioning central government since 1991.

Rival Islamist factions⁹ are battling forces loyal to the weak UN-backed government, which controls only small parts of the capital Mogadishu.

One of these groups, al-Shabab, is viewed by the Americans as al-Qaeda's proxy¹⁰ in Somalia.