Britain's Prime Minister David Cameron pledged support on Friday for Afghanistan's newly sworn-in president and the country's new unity government, saying during a surprise visit to Kabul that Britain is committed to helping Afghans build a more secure and prosperous future.

Cameron was the first of the world leaders to meet Ashraf Ghani Ahmadzai, Afghanistan's second elected president, since his inauguration on Monday. The two had a meeting in Kabul on Friday morning and later held a joint news conference.

"Britain has paid a heavy price for helping to bring stability to this country," Cameron said, paying tribute to the 453 British servicemen and women who died while serving in Afghanistan.