Bomb attacks in Northern Ireland have doubled over the last year, police figures showed on Thursday, evidence that dissident pro-Irish nationalists have stepped up activities to try to derail political stability, according to Reuters. A 1998 deal largely ended three decades of violence but small groups of dissidents say nationalists betrayed their cause by entering politics alongside pro-British unionists instead of pressing a fight for full independence from Britain. A local election last week boosted the status quo when the ruling coalition was returned with a greater majority. The Police Service of Northern Ireland (PSNI) said 99 viable bombs either exploded or were defused by army experts in the year to the end of March, compared with 50 a year ago. The security threat level stands at severe and police officers -- especially Catholics who have been encouraged to join the force -- have been targeted. At the beginning of April, a car bomb killed a 25 year-old Catholic constable. One man has been charged in connection with the bombing and a woman is being questioned by detectives. Ronan Kerr was the second Catholic officer to be murdered in two years, several more have been severely wounded or had narrow escapes. Security chiefs fear the dissidents will launch new attacks on either side of the Irish border to coincide with next week's visit to the Irish Republic by Queen Elizabeth -- the first by a British monarch since Irish independence nearly a century ago. One dissident group, the Real IRA, used an Easter message to oppose the visit, saying she was wanted for war crimes. The PSNI have loaned a specially adapted bomb and bullet proof Range Rover to the Irish authorities for the Queen to travel in during her four day visit. Thursday's police figures show that 188 people were arrested under the Terrorism Act, compared with 169 the year before. Those charged rose to 40 from 36. As well as bombings there were 72 shooting incidents, 33 casualties resulting from paramilitary style shootings and 81 paramilitary style assaults. Ordinary crime has hit a 13 year low and Chief Constable Matt Baggott said that was a reflection of the increasing acceptability of the PSNI in largely Catholic areas where the police were traditionally viewed with hostility.