Haiti's Prime Minister Garry Conille has submitted a resignation letter to President Michel Martelly, several sources said on Friday.

Conille's resignation comes amid political infighting between the two leaders over a parliamentary commission investigating whether some government ministers hold dual citizenship, which is illegal under Haitian law.

There was no immediate comment from the office of the president or the prime minister.

Conille, a medical doctor and U.N. development expert who took office just four months ago, has been under mounting pressure from Martelly.

The two have clashed over several issues, including an investigation of contracts awarded in the wake of the January 2010 earthquake that devastated Haiti in addition to the dual nationality issue.

The international community has sought to defuse the political tensions.

The head of the U.N. peacekeeping mission in Haiti issued a statement on Thursday expressing concern over a recent series of repeated crises between the executive and legislative powers that undermine the proper functioning of the institutions and the democratic process.

Mariano Fernandez, the special representative of the U.N. Secretary-General in Haiti, added that the political deadlock and institutional paralysis between the government, Parliament and the president ... are not likely to create the necessary conditions for recovery of the economy and the consolidation of democracy.

(This version corrects spelling of prime minister's name to Garry instead of Gary)

(Additional reporting by David Adams in Miami; Editing by Kevin Gray and Christopher Wilson)