"Today, Britain will announce additional troops for Afghanistan, bringing our numbers in Afghanistan to the highest level," the premier said at a joint news conference in London with U.S. President George W. Bush.
Brown did not give further details, but earlier British media reports said the country would send an additional 300 troops, bringing the total to more than 8,000.
Most British troops in the war-torn country are based in the southern Helmand province.
Brown added that Secretary of State for Defense Desmond Browne would make an announcement later in the day on the exact date that the troops were to be dispatched and their total number.
Over 100 British troops have been killed in Afghanistan since the start of the U.S.-led military operation that toppled the radical Islamic Taliban movement in October 2001. Most of the troops have died since 2006, when Taliban forces began stepping up attacks.
President Bush, who is on a farewell tour of Europe before leaving office in January 2009, praised Brown for the "steadfastness and resolution that he has shown in rooting out terrorism in all parts of the world".
