Other clashes in the region between DR Congo forces and Ugandan rebels as well as a local militia claimed eight more lives, the army said.

A DR Congo naval patrol was "attacked this morning by a Ugandan patrol boat in Congolese waters," Donat Kibwana, the administrator of the Beni region in the eastern province of Nord-Kivu said.

"The Ugandan boat sank and four troops and three Ugandan civilians are dead," he said. "On the Congolese side, a soldier and a civilian have been injured."

The clash took place near the Congolese village of Kyavinyonge on Lake Edward.

There has been no confirmation from the Ugandan side so far.

Kibwana said clashes between the forces of the two neighbouring countries had multiplied since the start of this month.

On Wednesday, a Ugandan patrol boat arrested 18 Congolese fishermen as they were casting their nets.

The Congolese navy is tasked with preventing militia fighters and local rebels and others from neighbouring Uganda and Rwanda from operating in the area.

Eastern DRC has been wracked by violence since the mid-1990s.

The Allied Democratic Forces (ADF) militia -- created by Muslim radicals to oppose the rule of Ugandan President Yoweri Museveni -- is one of a number of armed groups fighting over the region's rich mineral resources.

On Thursday, three members of the local Mai-Mai militia were killed at Kanyihunga, about 50 kilometres (30 miles) north of Lake Edward after they attacked an army post, Captain Mak Hazukay, the regional army spokesman said.

Hazukay said five ADF rebels died in Mwalika in Nord Kivu in clashes with the army.

The group stands accused of killing hundreds of civilians over the years and of carrying out a deadly attack on UN troops in Beni last December that left 15 peacekeepers dead.