Haiti President Michel Martelly promised Friday to move swiftly to fill the political void left by the surprised resignation of his prime minister and to implement critical reforms demanded by the international community.

Martelly’s promises to hold senatorial elections and revive an expired commission overseeing billions in earthquake aid, among others, came as the international community expressed deep “regret” and concerns over the resignation of Prime Minister Garry Conille, a gynecologist and former U.N. diplomat, after only four months.

A protracted political battle over Conille’s replacement not only puts Haiti’s fragile stability at risk two years after a devastating earthquake, but it gravely endangers attempts to secure foreign investments and desperately needed funds for its recovery. In past years, donors have held back dollars until a working government is in place.

“I regret that it’s at this moment when the country is taking off,” that Conille has resigned, Martelly said in brief address to the nation Friday night. Saying he was working to improve relations with parliament and to find a replacement, he urged Haitians and the international community “to stay calm.”

For weeks, Conille and Martelly, a former singer known as ‘Sweet Micky,’ had been at odds, disagreeing over how to handle a Senate commission charged with investigating the nationality of government officials including both of them; an audit of $300 million in post-earthquake contracts and who controls government ministers.

In recent days, pressure for Conille to resign mounted as senators close to Martelly threatened him with a confidence vote in parliament, and presidential advisers personally asked him to step down.

On Thursday, rumors circulated that Martelly would formally ask for Conille’s resignation in a letter. Less than an hour before he was scheduled to appear at the National Palace for an 11 a.m. meeting with Martelly and government ministers, Conille had his resignation letter hand delivered.

“We are muddling through from crisis to crisis,” said Robert Fatton, a Haiti expert at the University of Virginia. “The immediate future is likely to be very turbulent and a major crisis may be in the making.”

The international community, which had worked unsuccessfully to get a truce in the political infighting, responded quickly to the resignation. Canada said “he inspired a great deal of hope” and urgently appealed to Martelly and parliament to move quickly to name and confirm a new prime minister.

Conille said he did what he thought was in the best interest of the country.

“I’ve always been committed to being part of the solution and not part of the problem,’’ he told The Miami Herald. “I hope that the president will work with parliament to quickly ensure we have a functioning government and continue to institute necessary reforms.”

For days, Martelly and his supporters had been trying to negotiate a replacement for Conille, say lawmakers. They include foreign minister Laurent Lamothe and the former interim director of the recovery commission Ann-Valerie Milfort. Another possible candidate is Florence Guillaume, minister of health. All are close to Martelly. And with the presidents of both chambers telling Conille as late as Thursday evening the votes did not exist for his ouster, it could be difficult for the president to get his choices through.