Stephane Dujarric, U.N. Secretary-General Kofi Annan's spokesman, said they were shot at a checkpoint in the capital, Port-au-Prince, Tuesday.
Further details were not immediately known.
The attack occurred a day after the world organization protested a defamation campaign against the U.N. Stabilization Mission in Haiti, known as MINUSTAH, warning it could threaten the mission.
The mission and its chief, the secretary-general's Special Representative Juan Gabriel Valdes, have been under increasing verbal attack in recent weeks.
In a letter sent last week to Haitian Prime Minister Gerard Latortue, Annan said the campaign was unacceptable, Dujarric said.
Annan called on Haiti's Transitional Government to publicly condemn the campaign, warning it also threatens free and fair elections.
Annan added all concerned in Haiti must work together in a sprit of mutual respect and close collaboration.
The lack of security has forced the postponement of elections four times and the U.N. operation in the Caribbean nation was further hampered just over a week ago with the suicide of the military head of the mission.
The world organization aims to stabilize the impoverished nation in order for free elections to help it on the road to recovery from recent political turmoil.