Keira Knightley and Salma Hayek are campaigning for women's rights in Afghanistan.

The actresses are among a number of celebrities who have put their name to a letter which has been sent to UK Prime Minister David Cameron ahead of International Women's Day on March 8, asking him to assure help in the country.

Afghanistan has a fragile political infrastructure, and while its people are embracing great change in 2014 - with elections and the withdrawal of international troops - many are concerned about how women, whose rights have increased a great deal in the last decade, will be treated in future.

The letter has been signed by Keira Knightley, Joseph Fiennes, Salma Hayek, Benedict Cumberbatch, Michael Sheen, Gillian Anderson, Grayson Perry, Dave Stewart and Adrian Lester. It states:

"It has taken true courage for Afghan women to defy the Taleban, to vote in elections, to work in high-profile jobs, and to send their children to school. But Afghan women have told Amnesty International that they are concerned the rights they have fought so hard to achieve could now be lost. In the last six months, numerous Afghan women committed to working for peace and development have been murdered, including four policewomen, a pregnant school teacher and a local government worker. We mustn't turn our backs on the women and girls of Afghanistan. We ask that you publicly insist on renewed commitments to women's rights from the new Afghan President when that person is elected. As Prime Minister your support sends a very clear message to the Afghan authorities as well as to the brave women working for the future of their country."

The letter forms part of a campaign by Amnesty to protect the women of Afghanistan from attack. For more information visit amnesty.org.uk/afghanistan