Haiti

(CNN) -- Haitian President Michel Joseph Martelly said late Friday he had accepted the resignation of Prime Minister Garry Conille, thanking him for his service and promising to move quickly to replace him.

Conille just assumed the position in October after being ratified by the country's Senate. His reasons for stepping down were not immediately clear.

"This morning, Prime Minister Garry Conille presented me with his letter of resignation, I accepted it. I take this opportunity to thank him for his commitment. Of course, I regret that the resignation occurs in the context of where the country stands," said Martelly.

The president asked domestic and foreign investors to keep calm and promised that the country's leaders are "committed to harmonizing our efforts for a quick resolution of this situation and proposing a new prime minister."

"Haitian people, you know you can count on me, as I can count on you. I made you promises; I will respect them," Martelly said.

Conille, a former United Nations development specialist, served as chief of staff for former President Bill Clinton when the latter served as special U.N. envoy in Haiti.

In that role, Conille was involved in international aid delivery to Haiti following the devastating earthquake in 2010.

"This resignation comes at a time when the Haitian people are eager to embark decisively on the path toward reconstruction, economic growth and the strengthening of the country's rule of law institutions," the spokesman for U.N. Secretary-General Ban Ki-moon said.

"The secretary-general urges the Haitian authorities to act in the interests of the Haitian people and appoint a new prime minister as soon as possible," he added.

Conille, a gynecologist, earned a master's degree in health administration from the University of North Carolina at Chapel Hill. He worked for the U.N. Development Program and is a protege of economist Jeffrey Sachs, director of The Earth Institute at Columbia University.

When he assumed the position in October, Conille was welcomed in many corners as someone knowledgeable about development challenges with experience in working with the global community.

Martelly's two previous prime ministerial nominees-- businessman Daniel Rouzier and lawyer Bernard Gousse -- had been rejected by the Haitian Senate. The inability to form a working government raised concerns about Haiti's ability to move forward after the earthquake.

The United Nations estimates the January 2010 earthquake affected nearly 3 million people and killed about 220,000. More than 1.5 million people were left homeless in a country that was already the poorest in the Western hemisphere and wracked by crisis.