Irish nationalist gangs hurled gasoline bombs at police after three alleged IRA dissidents were arrested on suspicion of killing two British soldiers in an attack designed to trigger wider violence in Northern Ireland. Police operating in armored cars and flame-retardant suits said none of their officers was injured during the rising mob violence on Saturday in the Irish Catholic end of Lurgan, a religiously divided town southwest of Belfast. Rioters also blocked the main Belfast-to-Dublin railway line that runs alongside the hardline Kilwilkie neighborhood of the town. Later, police said they arrested a 37-year-old man and 30-year-old woman, and seized a gun and ammunition in the neighboring town of Craigavon, where Irish Republican Army dissidents shot to death a policeman Monday. Police would not say whether those arrests and the arms find were connected to the March 7 shooting of the soldiers or the subsequent killing of the policeman. Police said the couple were being questioned about unspecified "serious terrorist crime." The unrest came in direct response to Saturday's arrest of Colin Duffy, 41, the best-known Irish republican in Lurgan. Police arrested two other suspected Irish Republican Army dissidents aged 32 and 21 in the overwhelmingly Catholic village of Bellaghy - all on suspicion of shooting to death two soldiers last weekend. Police arrested two teenage rioters and advised motorists to stay away from the Catholic north side of Lurgan to avoid having their cars seized and burned as road barricades. An Associated Press reporter driving through the area at dusk Saturday night had to make a rapid escape to avoid youths - some wearing masks or with scarf-covered faces - hurling rocks and bricks in an apparent attempt to stop his vehicle. Police long considered Duffy the IRA godfather of Lurgan and twice charged him with murders in the town in the run-up to the IRA's 1997 cease-fire - which breakaway factions are now trying to destroy. Duffy was convicted of killing a former soldier in Lurgan in 1993, but was freed on appeal three years later after the key witness against him was identified as a member of an outlawed Protestant gang. He was back behind bars within a year after police identified him as the gunman who committed the IRA's last two killings before its cease-fire: two Protestant policemen shot point-blank through the backs of their heads while on foot patrol in Lurgan in June 1997. The prosecutors' case against Duffy collapsed after their key witness suffered a nervous breakdown and withdrew her testimony. Two years later, Protestant extremists assassinated Duffy's lawyer, Rosemary Nelson, with an under-car booby trap bomb in a case still being investigated today because of allegations that police were involved. Saturday's arrest of Duffy appeared likely to pose a political challenge for Sinn Fein, the IRA-linked party that is the leading Irish nationalist voice in Northern Ireland's power-sharing administration - and is trying to convince Protestants of its newfound support for British law and order. The leading Sinn Fein member of the coalition, Deputy First Minister Martin McGuinness, earlier this week denounced IRA dissidents as "traitors" and pledged to support the police's hunt for the gunmen. But previously, Sinn Fein has defended Duffy as an innocent man and a victim of British conspiracies. Sinn Fein declined to comment on the arrests. McGuinness was traveling Saturday in the United States and could not be reached for comment. Saturday's arrests came a week after the Real IRA splinter group fired more than 60 bullets at several unarmed, off-duty soldiers outside an army base as they collected pizzas, the first of two deadly gun attacks against British security forces. Two soldiers, aged 21 and 23, died and four other people were seriously wounded, including both pizza delivery men - whom the Real IRA described as legitimate targets because they were "collaborating" with the enemy. Police said the attack involved two masked men armed with assault rifles and a getaway driver. The IRA dissidents next struck Monday when Constable Stephen Carroll, 48, was shot fatally through the back of the head as he sat in his police car in Craigavon, the town beside Lurgan. A different splinter group, the Continuity IRA, admitted responsibility for that killing. Three people - a 17-year-old boy and two men - have been arrested since Tuesday on suspicion of involvement in killing the policeman. All remained in custody Saturday. The dissidents insist they have no intention of stopping attacks on British security forces and the civilians who work with them. The IRA pursued the same policy during its own 1970-97 attempt to force Northern Ireland out of the United Kingdom. Most IRA members agreed to renounce violence and disarm in 2005.