DUBLIN, Ireland — A special police detective unit will reopen investigations into 1,800 killings from Northern Ireland's bloody past, Britain and the province's police chief announced Tuesday.

The decision follows years of complaints from victims' relatives that British authorities had given up on solving many killings, particularly those committed by Northern Ireland's rival paramilitary groups.

Britain's governor for Northern Ireland, Paul Murphy, said the government had committed the equivalent of $57 million to form a special team of detectives led by officers from outside Northern Ireland.

"This is a huge project," Murphy said.

Murphy estimated the effort to identify those responsible for about 1,800 killings from 1969 to 1998 — accounting for more than half of the death toll from Northern Ireland's conflict — would run for six years.

Under the 1998 peace accord for Northern Ireland, anybody linked to a truce-observing group who is convicted of a politically motivated killing is eligible for speedy parole. This makes reopening most murder investigations in Northern Ireland more a question of revealing the truth than achieving justice.

Most parties welcomed the decision, even though Murphy said he did not expect many prosecutions or convictions to come from the work, in part because of little evidence. In some cases, detectives are expected to use modern DNA analysis on decades-old evidence to identify the killers.

Irwin Montgomery, chairman of the Northern Ireland Police Federation, said he hoped that new investigations would "bring closure" to the families of 211 officers whose killings — largely committed by the outlawed Irish Republican Army — remain unsolved.

"Families just want to know what happened to their loved ones. They want to know the circumstances of their deaths," he said.

But Relatives for Justice, a pressure group representing many of the approximately 350 people killed by British troops or Northern Ireland police since 1969, rejected the plan.

Group spokesman Mark Thompson said the detective unit would operate under the immediate control of the Northern Ireland police force and the ultimate authority of the British government. He said Britain "protects its interests and investigates itself."

But Northern Ireland's police commander, Chief Constable Hugh Orde, said he operated independently of the British government, while the detectives would be drawn from other parts of the United Kingdom and even the Republic of Ireland.

The Police Service of Northern Ireland and the republic's police force, the Garda Siochana, last month signed an agreement that allows officers from both forces to work in each others' jurisdictions on temporary assignments for the first time since Ireland was partitioned in 1921.

Murphy said the unit's commander would be Dave Cox, a recently retired senior officer in London's Metropolitan Police.

A moderate Catholic politician, Alex Attwood, said the new investigation must address the fact that, in many cases involving the killing of Catholics, relatives believe the original investigations by Northern Ireland's mostly Protestant police were inadequate.

But he said the effort to reopen investigations offered "remarkable contrast" to the policies of Northern Ireland's underground groups, chiefly the IRA and the Ulster Defense Association, the major anti-Catholic group.

Those groups, Attwood said, "refuse to account for their actions and insult the memory of many families and many in the community by refusing to acknowledge killings as murder and widespread human rights abuses as crimes."

He was referring to the IRA's claim that its activities, including killings and the deliberate maiming of suspected criminals, are not crimes.

About 3,400 people have died in politically motivated violence in Northern Ireland since 1969, when British troops were deployed as would-be peacekeepers following riots between the British Protestant majority and Irish Catholic minority.

A newly formed Provisional IRA, rooted in Catholic areas, killed about 1,800 people before calling a 1997 truce, while other anti-British groups killed more than 200. Anti-Catholic groups from hard-line Protestant areas killed about 1,000, while others died in unclear or disputed circumstances.