The US is to send another 4,000 sailors and marines to Haiti for the earthquake relief mission.

The additional troops will be diverted from deployments in Africa and the Gulf. The navy says they will "significantly" increase the ability to provide aid quickly.

This will bring the total number of US troops in Haiti to 16,000.

According to aid groups, the relief effort remains largely uncoordinated, with long delays in getting vital supplies of food, water and medicine to survivors.

Medicins Sans Frontieres (Doctors Without Borders) said its cargo plane, containing medical supplies, had been turned away from the airport three times since Sunday.

Haiti's president, Rene Preval, said aid delivery was the main problem: "When it arrives, the question is: where are the trucks to transport it, where are the depots?"

A strong aftershock hit Port-au-Prince yesterday, but reportedly has not caused further casualties.

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