LONDON, England (CNN) -- The United Kingdom will send an additional 500 troops to Afghanistan in early December, bringing the British contingent there to more than 9,500, Prime Minister Gordon Brown announced in the House of Commons on Monday.

"We must address the terrorist threat at its source," Brown said, adding: "Our task is to prevent the Taliban from giving al Qaeda ... safe haven.

"Instability in Afghanistan can only increase the risk of conflagration where the rest of the world can least afford it."

Brown regularly links British security to events in Afghanistan and Pakistan, saying attacks on London and other British targets have been planned in south Asia.

He announced in October the decision in principle to boost force levels, but said certain conditions -- including proper equipment for the British troops and more troop commitments from other countries -- had to be met first.

The United Kingdom has the largest contingent in Afghanistan after the United States. The figure of 9,500 does not include special forces, said Brown, who declined to say exactly how many are there, but indicated it is more than 500.

The-CNN-Wire/Atlanta
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