Northern Ireland\'s police were on high alert Saturday as they warned that terror groups could launch deadly attacks over the Easter holidays. In an unusual move, the province\'s police force warned the public to be extra vigilant \"due to the severe threat level posed by terrorists\". The Police Service of Northern Ireland (PSNI) said it believed dissident terror groups were \"intent on trying to murder officers in the coming days\". The warning comes after rookie Catholic police officer Ronan Kerr was killed in a car bomb attack on April 2 and the discovery of a massive car bomb left in an underpass beneath the main road linking Belfast and Dublin on April 7. Authorities fear dissident republicans opposed to the peace process are increasing attacks ahead of May 5 elections in the province and a visit by Queen Elizabeth to the neighbouring Republic of Ireland from May 17 to May 20. \"Dissident terrorist groups are continuing to identify officers and target them with the single objective of killing them. And, in so doing, their reckless actions will also put the lives of our wider communities at risk,\" a PSNI spokesman said. \"The public will see an increased visible police presence over the coming days and weeks and we ask for their patience with their officers if they are inconvenienced due to police activity. \"We are taking these steps to keep communities and their officers safe. We would not do this if it was not absolutely necessary to protect life.\" The public alert, issued on Good Friday, comes 13 years after the Good Friday agreement, which largely ended three decades of sectarian bloodshed and put the province on the path to peace between Protestants and Catholics. It also comes as thousands of mainstream Catholic republicans supporting the peace process prepared to hold dozens of commemoration parades to mark the 1916 Easter Rising against British rule. Three men were arrested Friday when police stopped a car in Keady, a town close to the Irish border. The PSNI described the arrests as \"significant\" and it is understood a number of undisclosed items were taken away for examination. The men were detained as part of a security operation which also involved police from the Republic. Meanwhile a 33-year-old man was to appear in court Saturday after being questioned by detectives investigating Kerr\'s murder. The suspect is accused of possession of firearms and explosives with the intent to endanger life and possession of articles likely to be of use in terrorism. A group claiming to be former members of the paramilitary Irish Republican Army claimed responsibility for Kerr\'s murder in a statement shown to the Belfast Telegraph newspaper. The IRA ended its armed campaign in 2005, though dissident splinter groups still persist. \"The will of Irish republicans to resist the forced occupation and partitioning of our country has not been defeated,\" the statement said. \"Irish republicans have continued to organise against the British presence in our country. We continue to do so under the name of the Irish Republican Army. We are the IRA.\"