The 51 migrants are reported to be from Eritrea

Malta is refusing to allow a Spanish trawler which picked up the migrants to dock, drawing criticism from the UN.

European Union Justice Commissioner Franco Frattini said he had spoken with Spanish, Italian and Maltese ministers.

He said the trawler had done a "fantastic" job but that Malta needed help to deal with migration pressures.

Pregnant woman

The Maltese government is insisting the Eritrean men, women and children on board are Spain's or Libya's concern, since the boat is Spanish and the rescue was made in Libya's search-and-rescue zone.

Our plan is to have at our disposal a permanent team of about 250 to 300 people... which will be able to intervene very quickly at the request of a member-state Justice Commissioner Franco Frattini EU plans rapid reaction border teams

A Spanish junior foreign minister, Bernardino Leon, said that two Spanish inspectors who boarded the vessel on Tuesday had reported that conditions for the immigrants were beginning to get worrying.

The AFP news agency says a pregnant woman and mother and child were temporarily taken off the trawler to receive medical treatment, but were taken back later.

The United Nations refugee agency, UNHCR, has told the Maltese authorities to let the migrants disembark urgently.

But the government of Malta says it has no more capacity to deal with illegal immigrants and has been pressing the EU to help.

EU mission

Mr Frattini said the European Union was about to launch a mission to patrol the Mediterranean near Malta, as he announced plans to set up a system for sending rapid reaction border guard teams to countries facing a migration crisis.

He added that the Spanish minister of foreign affairs had proposed a solution to the current standoff, but he said he did not want to predict what the final outcome would be.

Almost 1,000 immigrants have landed on Malta, which has a total population of 400,000, since January.