Lieutenant commander Sampath Hettiarachchi was wanted in connection with the abduction and illegal detention of 11 young men between 2008 and 2009, police said, the final phase of the war between government forces and ethnic Tamil separatists.

The 11 men are believed to have been killed while being illegally held by the navy. Their bodies were never found.

The then-navy spokesman D.K.P. Dissanayake is also a suspect in the case. He was arrested last year and is currently on bail.

"We have now arrested one of the most wanted men and we are very close to concluding the investigation," a police source said, adding that Hettiarachchi was also wanted in connection with the 2006 slaying of Tamil lawmaker Nadarajah Raviraj.

There have been persistent allegations that senior military personnel and members of the former regime of strongman president Mahinda Rajapakse were responsible for a number of high-profile killings.

Several military intelligence officers are facing prosecution in connection with the assassination of a prominent anti-establishment newspaper editor, and for orchestrating attacks on other journalists and dissidents during Rajapakse's rule that ended in January 2015.

The former leader and several members of his family are also being probed for large-scale financial fraud and murder during his decade as president.

Rajapakse successfully crushed the separatist rebels, known as the Tamil Tigers, but the government offensive also sparked allegations of widespread abuses, including the killing of 40,000 minority Tamils by the ethnic Sinhalese-dominated armed forces.