Keira Knightley and Salma Hayek are among a host of celebrities who have written to British Prime Minister David Cameron about women's rights in Afghanistan. The Pirates of the Caribbean actress was joined by actors Joseph Fiennes, Benedict Cumberbatch, Michael Sheen and Gillian Anderson in signing a letter to the U.K. leader ahead of International Women's Day on Saturday (08Mar14). The note - written in partnership with campaign group Amnesty International - urges Cameron to make sure women's rights in Afghanistan are protected in 2014 despite presidential elections and the withdrawal of international troops. The letter reads, "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."