BELFAST (AFP) - A 17-year-old boy was due to appear in court in Northern Ireland on Tuesday charged with the murder of a policeman, an attack which fuelled fears of a return to the province's bloody past.

Police charged the teenager late Monday following the shooting of on-duty Constable Stephen Carroll in Craigavon, southwest of Belfast, on March 9.

It was the first time since 1998 that a police officer had been killed in the province, and the murder came within 48 hours of the fatal shootings of two British soldiers.

The unnamed 17-year-old was charged with murder and possessing a firearm with intent to endanger life and with "collecting information likely to be of use to terrorists," police said.

He was also charged with belonging to the Continuity IRA (Irish Republican Army) - a banned republican splinter group dedicated to achieving a united Ireland through violence which claimed responsibility for Carroll's murder.

The youth was due in court in Lisburn, southwest of Belfast.

He was arrested on March 10 around 100 metres from the scene of the crime. Police dressed him in a forensic white body suit and drove him away for questioning before seizing his car.

Carroll, 48, was shot in the back of the head as he checked out reports of a brick thrown through a window.

Seven people were originally arrested over the murder, but two were released Monday without charge.

Carroll's funeral was held on March 13. It was attended by churchmen from Northern Ireland's four main Christian denominations and political parties, its police chief Hugh Orde and ministers from London and Dublin.

Four people remain in custody, meanwhile, over the March 7 killings, claimed by the Real IRA, another splinter group, of the British soldiers at the gates of the Massereene Barracks in Antrim, northwest of Belfast.

Six of those being held over the three murders will challenge their extended detention in the High Court in Belfast on Tuesday, arguing it breaches their right to liberty under the European Convention on Human Rights.

They are the first people to be held in Northern Ireland under the Terrorism Act of 2006, which means they can be held for up to 28 days without charge.

Northern Ireland's human rights commissioner Monica McWilliams has visited the Antrim police station where the suspects are being held to inspect the conditions.

"We have always been against these lengthy detention periods so the issue would be to charge people or to release them now after this length of time," she said.

"Some of them have not even been interviewed for a number of days now."

More than 3,500 people died in three decades of civil strife in Northern Ireland, known as the Troubles, before the Good Friday Agreement in 1998 led to power-sharing in the province between the Protestant majority and the Catholic minority.