Haiti's government had hoped that the rice subsidy as well as Parliament's firing of Prime Minister Jacques Edouard Alexis on Saturday would defuse rage over rising food prices that has produced days of deadly rioting and looting.

But later on Saturday, a Nigerian UN officer bringing food to his unit was pulled from a car and killed execution style with a gunshot to his neck in Port-au-Prince, UN officials said.

The officer, identified in a forensics report as Corporal Nagya Aminu, 36, drove a marked UN vehicle into a crowded clothing market near the cathedral before he was attacked, UN police spokesman Fred Blaise said.

The incident is the first execution-style killing of a UN peacekeeper since the mission came to Haiti in 2004.

Two Haitian men were detained for questioning, including a local television journalist who was covering the incident.

Many in the crowd chanted 'Down with MINUSTAH', referring to the UN mission by its French acronym, even as several market stalls were set on fire after the killing.

The attack came hours after Haitian lawmakers ousted Mr Alexis, whom they blamed for not boosting food production and refusing to set a timetable for the departure of UN peacekeepers.

'I think that will satisfy the people,' opposition senator Youri Latortue said after 16 senators out of 27 voted to remove the prime minister on Saturday.

President Rene Preval immediately said he would seek a replacement for the ousted Mr Alexis, who took office in 2006.

About 25 people gathered outside Parliament after the dismissal, chanting 'Aristide or death', referring to exiled former president Jean-Bertrand Aristide.

Some residents felt their plight would not improve regardless of the dismissal of the prime minister.

'Alexis left? What's the difference?' asked Mr Jackson Aubri, a 28-year-old chicken vendor.

Earlier in the day, Mr Preval had announced a more than 15 per cent cut in the price of rice.

Globally, food prices have risen 40 per cent since mid-2007.

Haiti has been particularly affected because it imports nearly all of its food, including more than 80 per cent of its rice.

ASSOCIATED PRESS