Brajesh Mishra, national security adviser and principal secretary to former prime minister Atal Bihari Vajpayee, has resigned, it was officially announced on Tuesday.

Prime Minister Manmohan Singh has accepted Mishra's resignation with effect from May 22, the announcement said.

Mishra had played a key role on several issues relating to domestic and international policies, including in forging closer ties with China and bringing thaw in India-Pakistan relations.

He was special representative for talks with China to expedite resolution of the border problem.