Prime Minister David Cameron paid a pre-Christmas visit to British troops in Afghanistan on Tuesday, although his plans were upset by a dust storm, officials and media said.

Cameron had intended to visit Camp Bastion in the restive southern province of Helmand, where the majority of Britain's 9,500 troops are based, but his Royal Air Force flight was forced to divert to Kandahar airfield.

Wearing a black fleece, khaki trousers and boots, the premier told reporters travelling with him that the change of plan was "disappointing" but welcomed the chance to meet some RAF pilots flying Tornado jets from the NATO base.

He was given a tour around one of the planes and also shared a cup of tea and a chat with soldiers and air personnel in their canteen.

A dust storm had enveloped the runway at Camp Bastion and forced its closure, causing the prime minister's plane to divert to the base in neighbouring Kandahar province.

He was also forced to cancel a planned meeting with the governor of Helmand in the provincial capital Lashkar Gah, and a visit to a frontline base.

However, Cameron called Afghan President Hamid Karzai and the two leaders agreed to meet in London early next year, probably January, to sign a strategic agreement, officials said.

During the conversation Cameron told Karzai the security situation in Helmand and Kandahar has "improved", a statement from the president's office said.

"Cameron... said that Britain wanted the continuation of the peace process and talks with the armed opposition," the statement said, referring to the need for reconciliation with the Taliban.

The prime minister had arrived in Afghanistan under a security-imposed news blackout for a trip aimed at boosting morale in the armed forces as they head into holiday season under pressure from military budget cuts and job losses.

In Kandahar, Cameron met US General James Huggins, the head of International Security Assistance Force Regional Command South, for talks on military progress in Afghanistan.

Britain intends to pull out all its combat troops by 2014, starting with 500 troops next year, and Cameron indicated more could be withdrawn in 2013 to avoid a sharp pull-out in three years' time.

"I don't want to see some massive cliff-edge in 2014 -- I don't think that's practical. But I don't think we need to make hard and fast decisions at this stage," Cameron told reporters.

A newspaper report earlier this month claimed Britain was mulling pulling out up to 4,000 troops before the end of 2013.

Cameron said there was "an ongoing conversation with our allies" about how and when NATO forces would be withdrawn.

"I'm absolutely clear that the British public deserve to know there is an endpoint to our involvement in Afghanistan and that endpoint is 2014," he said.

Cameron last visited Afghanistan in July, when he managed to get to Camp Bastion but decided to scrap a visit to Lashkar Gah after a British soldier went missing from a checkpoint in Helmand and was later found dead.

A total of 391 British troops have died in Afghanistan since the US-led war against the Taliban regime began following the September 11, 2001 attacks.

Tuesday's visit coincided with the announcement of a new British governmental committee designed to protect the interests of the armed forces, from the pay of serving soldiers to the education of their children back home.

Cameron, who will chair the committee's inaugural meeting in January, said: "There will always be an ongoing debate about what more we can do as a nation to thank and reward people who serve the crown in this way."