Pakistan's ambassador to the United States has stepped down following claims he appealed for Washington's help in reining in Pakistan's powerful military.

Ambassador Hussain Haqqani resigned Tuesday following a meeting with Pakistani Prime Minister Yousuf Raza Gilani and army and intelligence officials in Islamabad. The prime minister's spokesman said Haqqani was asked to step down so that an investigation can be properly carried out.

Haqqani has denied drafting a memo calling for U.S. help in preventing a military coup in Pakistan following the American raid that killed former al-Qaida leader Osama bin Laden. The letter was sent in May to Admiral Mike Mullen, the top U.S. military official at the time.

The controversy exposed the long-running power struggle between Pakistan's civilian government and the military, which has ruled the country in the past.

Pakistani-American businessman Mansoor Ijaz described the memo in an opinion piece published last month in the Financial Times newspaper.

In return for U.S. help in preventing a military coup in Pakistan, the memo said a new national security team would conduct a full inquiry into allegations that Pakistan harbored bin Laden. The new team would also hand over top al-Qaida members and ensure that Pakistan's military spy agency cuts ties to the Taliban, the Haqqani network and other groups.

Ambassador Haqqani said Tuesday that he was resigning to bring closure to the “meaningless controversy threatening our fledging democracy.” He added on Twitter that he has “much to contribute to building a new Pakistan free of bigotry and intolerance.

Haqqani had been Pakistan's envoy to the United States since 2008 and was well-regarded in Washington. He is a close ally of Pakistani President Asif Ali Zardari.

It is unclear who will replace Haqqani as ambassador.