British soldiers set off on an operation in Helmand province in Afghanistan. (Omar Sobhani/Reuters)

Britain will add at least 350 more troops to its mission in Afghanistan if other allies bear their share of deployments, says Prime Minister Gordon Brown.

Brown laid out his plan for Britain's role in Afghanistan in a speech in the House of Commons on Wednesday.

Though Brown did not give a specific number on the additional troops, he said the British contribution would be increased to about 9,500. Britain currently has about 9,150 troops in Afghanistan.

The decision to deploy additional troops and equipment comes on the advice of commanders on the ground, Brown said.

No date has been set for when the troops will be deployed.

The condition attached to the additional British deployment was likely directed at the United States, which is currently considering its role in Afghanistan.

"Future operations, the protection of population, populated areas, must be the shared responsibility of Afghan and coalition forces," Brown said. "This will be central to the new benchmarks and timelines we and Gen. McChrystal will set out as part of a new framework for the transition to Afghan authority."

British Prime Minister Gordon Brown leaves his official residence, 10 Downing Street, for the new parliamentary year on Wednesday. (Akira Suemori/Associated Press)

U.S. officials have said NATO's top commander in Afghanistan, U.S. Gen. Stanley McChrystal, has requested his country send up to 80,000 more troops.

U.S. President Barack Obama said Tuesday he would decide in "the coming weeks" on a war strategy and the troops needed to carry it out.

Brown said he supports McChrystal's drive to accelerate the growth of the Afghan security forces.

The prime minister held discussions in recent weeks with Obama and NATO Secretary General Anders Fogh Rasmussen, as well as with U.S. and British generals to discuss future strategy in Afghanistan before announcing his decision in Parliament.

Britain's army chief Gen. David Richards had previously said the U.K. is prepared to send more forces.

Brown has previously told legislators that he wants to accelerate the British mission to focus on training Afghan police and soldiers.

Ahead of the speech, analysts had said Brown would likely increase troops to the war-torn country by about 500.

"I think we probably do need more than that, but it's a contribution," Britain's former commander in Afghanistan, Col. Richard Kemp, told the BBC.

Britain's mission in Afghanistan has become increasingly unpopular as casualties mount. A total of 221 U.K. military personnel have died in Afghanistan since the war there began in late 2001, according to the Ministry of Defence.

Kemp said the additional manpower would allow military chiefs to deploy an extra battle group into central Helmand province, something he said would give commanders there "extra combat power."

With files from The Associated Press