Tensions flared in Northern Ireland yesterday when masked gangs attacked police with petrol bombs, bricks and stones after a dissident republican was arrested in connection with the murder of two soldiers last week.

Colin Duffy, 42, is a former IRA prisoner who stood trial in the 1990s for the murder of a soldier but was acquitted when it emerged that a key witness against him was a loyalist paramilitary.

Following his arrest yesterday, gangs took to the streets near his home in Lurgan, Co Armagh, and members of the Police Service of Northern Ireland (PSNI) were pelted with stones before petrol bombs were hurled at their vehicles. A tense stand-off developed last night with youths forming makeshift barricades to block the railway lines in the town.

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Also arrested in the Craigavon area last night in connection with the murder were a 30-year-old woman and a 37-year-old man. Detectives are now questioning five people over the murder.

Two other men, aged 21 and 32, were also arrested after police raids in Lurgan and Bellaghy, Co Londonderry, in connection with the killings of the two soldiers last week.

Sappers Mark Quinsey and Patrick Azimkar were shot dead last Saturday by the dissident republican Real IRA as they collected pizzas at the gates of the Massereene barracks in Antrim.

Mr Duffy broke away from mainstream republicanism in opposition to Sinn Fein's decision to back the new PSNI in 2007, and became a member of the republican protest group Eirigi, which insists it is a peaceful pressure group opposed to the new police.

He has been a high-profile and controversial figure in the feuding world of Northern Ireland politics for nearly two decades. He was charged four times with terrorist offences, including murder, and was acquitted each time, once on appeal.

In 1990, he was charged with possessing 10 bullets. He was granted bail but when he left the barracks of the then Royal Ulster Constabulary he was followed by a hit squad who opened fire on him and his two co-accused. Mr Duffy survived but one of his co-accused, Sean Marshall, was killed.

In 1997, Mr Duffy walked free from court after charges over the killings of two RUC constables in Lurgan were dropped when the Director of Public Prosecutions said there was less than a "reasonable chance" of conviction. His solicitor, Rosemary Nelson, received threats after representing him in court. She was murdered in a loyalist car bomb attack in 1999.

In 2001, his home was raided by police, who removed his shoes for forensic analysis. They were investigating the 1989 murder of Roy Metcalfe, 40, a Protestant owner of an army surplus store, who was shot 18 times. Police had found a pair of boots at the scene.

Last year Mr Duffy attracted criticism when rioting broke out in the Lurgan area, leading to gun and petrol bomb attacks on the police. He said the attacks were due to a section of the nationalist community refusing to accept the PSNI.