The van was seized Sunday night, The Irish Times reported. Officers with the Police Service of Northern Ireland arrested the driver, a man on a motorcycle who was following the van and a third man who was picked up at his home early Monday morning.
Chief Superintendent Stephen Cargin said the intended target is believed to have been the Londonderry police headquarters. He said the mortar bombs were in tubes, fully primed and ready to be launched.
"But for the excellent work of officers whose job is to protect the community we could well have been looking at a scene of mass casualties and multiple deaths today, not just of police officers but also of members of the community who live close to the intended target, which we believe with certainty was to have been a police base," he said.
Police sources told the Times the attack was foiled by a joint investigation involving the PSNI and the Garda, the Irish National Police. While the men who were arrested, believed to be dissident republicans, live in Northern Ireland, the van was registered in Dublin.
Politicians on both sides of the border denounced the attack. Deputy First Minister Martin McGuinness of Sinn Fein, the leading republican party, said there is "no going back to the past," InsideIreland.ie reported.
"The community in Derry City and elsewhere simply will not allow it," he said. "This is not about any attempt to advance a united Ireland. This is a vanity trip by those involved and more about money and ego than patriotism."