Britain and the US are to join forces to tackle the "evolving threat" from Islamist groups in Yemen and Somalia, Downing Street has announced.
Officials said the UK and the US would jointly fund a counter-terrorism police unit in Yemen in the wake of an alleged 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 airliner 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 and potential safe haven for terrorism" and said it presented "a regional and global threat".
The UK is one of Yemen's leading donors and is already helping 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."
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 spotlight 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 factions 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 proxy in Somalia.
Security review
The Downing Street statement set out Mr Brown's other intentions:
• Have the evolving threat from Yemen and Somalia placed on the agenda for the EU General Affairs Council in January
• Push for stronger action on Yemen from the Financial Action Task Force
• Discuss further the UK's response to the suspected bomb plot at a special meeting of the National Security, International Relations and Development committee (NSID)
The alleged bomber, Mr Abdulmutallab, who is now in US custody, is accused of trying to detonate a bomb on a flight as it came in to land.
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The 23-year-old allegedly attempted to ignite explosives stored in his underpants. He had flown from Accra in Ghana to Lagos in Nigeria, where he boarded a flight to Amsterdam before changing planes for Detroit.
The mid-air drama on 25 December has sparked a worldwide aviation security review.
Both Mr Obama and Mr Brown have ordered urgent reviews of airport security, with UK officials expected to report back with preliminary findings "in days".
The prime minister has pledged to "move quickly" to improve security wherever necessary and suggested new technologies such as full body scanners may become more widely used at UK airports.
He has also called a summit in London to discuss radicalisation in Yemen.
No 10 said the 28 January event had support from Washington and the European Union, and Mr Brown aimed to attract Saudi Arabia and Gulf states.
On Saturday, Mr Obama for the first time publicly accused an offshoot of al-Qaeda over the alleged plot.
In his weekly radio and video address posted on the White House website, Mr Obama said: "We know that [Mr Abdulmutallab] travelled to Yemen, a country grappling with crushing poverty and deadly insurgencies.
"It appears that he joined an affiliate of al-Qaeda, and that this group, al-Qaeda in the Arabian Peninsula, trained him, equipped him with those explosives and directed him to attack that plane headed for America."
The group said it was behind the alleged attack in an internet statement last week.