He made the announcement during his first visit to Afghanistan since the formation of the Coalition Government.
During a joint press conference with Afghan President Hamid Karzai in the capital Kabul, the PM said an additional £67 million will be provided to troops to help them counter improvised explosive devices (IEDs).
He also announced additional funding for policing, education, jobs and governance reform in Afghanistan.
The PM said:
My biggest duty as Prime Minister of the United Kingdom is to our armed forces and to make sure that they have all the equipment and all of the protection that they need to do the absolutely vital job that they are doing here in Afghanistan.
I’m pleased to announce today that we will be spending an extra £67 million on countering the IED threat and actually doubling the number of British teams that are there to counter the threat from those explosive devices.
Mr Cameron emphasised the importance of the relationship between the two countries and that Afghanistan is Britain’s most important foreign policy and national security issue.
He added that this year will be a “vital year” when Nato forces have to make progress - both for the sake of the Afghan people and on behalf of people in Britain “who want to see this work and want to see progress”.
The two leaders also met last month and held talks at Chequers where they agreed that the relationship between Afghanistan and Britain should be further strengthened.
Foreign Secretary William Hague, Defence Secretary Dr Liam Fox and International Development Secretary Andrew Mitchell also visited Afghanistan last month. They met President Karzai, relevant Ministers and senior officials in a bid to gain a better understanding of the situation in Afghanistan.
Read more about the visits by Mr Hague, Dr Fox and Mr Mitchell on the Foreign Office website.