The activists said US immigration policy was racist, highlighting the difference in the treatment of Haitian and Cuban migrants.

Cubans are generally allowed to remain in the US if they reach shore, under the "wet-foot/dry-foot policy". But under an agreement with Haiti, those who arrive without proper documentation are deported.

Several people have highlighted the case of Elian Gonzalez, a six-year-old Cuban boy who was brought ashore after a boat of immigrants capsized. He is living with relatives in Florida while his father and the Cuban Government seek his return.

"The way INS (Immigration and Naturalisation Service) has treated Elian probably gave hope to other people, especially Haitians who have a tradition of going to sea to escape terrible conditions at home. We are being treated differently for the reason of our skin colour," said Herntz Phanord, host of a Haitian programme on WLQY.

The 411 migrants - including 16 Dominican and two Chinese - attempted to come ashore in Florida in the early hours of New Year's Day on board a dangerously overcrowded wooden boat. The INS was not swayed by local politicians' demands to consider the refugees' request for asylum.

All but four were sent back to Haiti overnight on Sunday on board two US Coast Guard ships. They are due to reach the Haitian capital, Port-au-Prince on Tuesday afternoon.

Legal challenge

"I'm very disappointed that INS once more has decided to continue its racist policy vis-a-vis the Haitians and failed once more to give them the right to a fair and due process," said Marleine Bastien, president of Haitian Women of Miami.

Immigrant advocacy groups are considering mounting a legal challenge to the wet-foot/dry-foot policy. Campaigners want to change the law so that all those who reach US territorial waters will get the chance to plead for asylum.

"I'd like them to eliminate this wet foot/dry foot policy. It's unfair to immigrants," said Ms Bastien.

"It's not a question of Haitians and Cubans. It's a question of respecting basic human rights."

After the boat ran aground on a sandbar, Coast Guard crews tossed life jackets on board and told the migrants that, no matter what, they would not be allowed to enter the US.

Four Haitian women - three of them pregnant - were brought ashore for medical reasons and remained in Miami for treatment at local hospitals.

Those four are expected to be returned later, said Mike Gilhooly, an INS spokesman.

In 1999, the Coast Guard rescued or turned back 363 Haitians and 406 Dominicans trying to reach the United States.