"The judge extended their detention by 14 days," said Birgitte Skjodt, a lawyer representing one of the four men.

The men were detained after a clash with the Danish navy in the Gulf of Guinea off the coast of Nigeria on November 24.

Four others were killed in the exchanges, Denmark's armed forces have said, while a ninth pirate fell overboard.

After their boat sank, the pirates were brought on board the Danish navy ship, where one of them had to have a leg amputated due to serious wounds.

Their nationalities were not immediately clear, but the Danish armed forces have said those detained at sea have spoken to their families in Nigeria.

It all started when the frigate Esbern Snare, which has been patrolling the area since early November, attempted to board the pirate boat. The Danish forces and the pirates exchanged gunfire.

Danish prosecutors accuse the pirates of firing the first shot and are seeking to press charges over them attacking Danish soldiers, accusations they deny.

The prosecution team also wants to bring the suspects to Denmark, but Denmark has not signed any extradition agreement with countries around the Gulf of Guinea.

Skjodt, whose client was gravely wounded in the incident last month, said the men had been acting in self-defence.

"The accused were sitting in a little... boat and felt attacked. It is therefore self-defence," she told public television broadcaster DR.

A piracy hotspot stretching 5,700 kilometres (3,540 miles) from Senegal to Angola, the Gulf of Guinea saw 195 attacks in 2020.

The same year, 130 of 135 hostage takings at sea occurred in the region, according to the International Maritime Office.

Copenhagen in March announced it was sending the Esbern Snare to patrol the zone, where some 40 Danish ships operate daily.