Moving quickly to fill a vacant ambassador post in Washington left by the resignation of Husain Haqqani, Pakistan unexpectedly appointed a former information minister and outspoken human rights campaigner as its new envoy.

Sherry Rehman is also serving as the chairperson of Pakistan Red Crescent Society (PRCS).

"The prime minister is pleased to appoint Sherry Rehman as the new ambassador to the United States," said spokesman for the Prime Minister's office.

Haqqani resigned on Tuesday, days after a Pakistani-American businessman accused him of being behind a memo that accused the Pakistani military of plotting a coup in May