By Ian Graham
BELFAST (Reuters) - Police in Northern Ireland said they had foiled an attempt to attack a police station with mortar bombs, seizing the weapons from a van in a residential area of Londonderry on Monday morning.
About 100 homes were evacuated in the province's second city as army bomb disposal officers prepared to remove four live mortar bombs, a police spokesman said.
"There would have been mass murder of police and serious damage to property" had the attack on a nearby police station succeeded, Chief Superintendent Stephen Cargan told BBC radio.
A 1998 peace deal largely ended more than three decades of violence in the British-controlled province between mainly Catholic Irish nationalists seeking union with Ireland and predominantly Protestant unionists who want to remain part of the United Kingdom.
But dissident nationalists still stage sporadic gun and bomb attacks which have intensified in the past four years as frustration with the power-sharing government established under the 1998 deal has grown in parts of the nationalist community.
Sinn Fein, the largest nationalist party in that government, condemned the attempted mortar attack.
"There is no place for these people who call themselves dissident republicans in the 21st century," said Raymond McCartney, a Sinn Fein deputy in Northern Ireland's regional parliament.
Police said they believed the bombs in the van were linked to militant nationalists. They arrested three men, including one in the van and one on a motorbike near by.
Chief Superintendent Cargan described the mortars as "crude home-made devices" that could easily have missed their intended target and hit nearby houses.
Several roads on the western outskirts of the city were shut while army bomb disposal experts worked at the scene, police said. Part of one of the city's main bridges was also closed.
Local nationalist politician Pat Ramsey told media police had been attacked with stones and at least one petrol bomb as they attempted to evacuate homes.
Several homes were evacuated after a second suspected bomb was found in Ballymena, a town north of Belfast, a police spokesman said. The device was later found to be a hoax.
Militants have targeted government offices in Londonderry in recent months in the run up to the city's 2013 term as UK City of Culture.
Discontent with Northern Ireland's power-sharing government in working-class Protestant areas fuelled weeks of rioting in December and January after nationalist councillors voted to end a century-old tradition of flying the British union flag every day over Belfast City Hall.
(Reporting by Ian Graham and Conor Humphries; Editing by Andrew Heavens)