Afghanistan's Karzai and Pakistan's Sharif meet in London

In a bid to help foster peace efforts, President Hamid Karzai will meet Pakistan's Prime Minister Nawaz Sharif in London this week.

President Karzai, who must step down next year after serving two terms, will also give a speech at the World Islamic Economic Forum, and at the Oxford Union, the university's debating society, during his four-day visit.

The BBC's David Loyn in Kabul explains the relationship between the two countries.