Explosion at N. Ireland base

BELFAST, Northern Ireland -- An explosive device has been detonated outside a military base in Northern Ireland's second largest city.

Police said the device was detonated at the front of a security force base in the centre of Londonderry on Friday morning. There were no immediate reports of damage or injuries.

On Tuesday, a mortar was fired at an army and police base in Bessbrook, south of Belfast, from a van parked nearby.

Nobody was injured and the mortar, containing 150 pounds of explosive, was defused by the bomb squad.

Nobody has claimed responsibility for either attack but they come after a series of bombs in London blamed by officials on the Real IRA, a group of Irish Republican Army dissidents who oppose Northern Ireland's 1998 Good Friday peace accord.

The U.S. State Department declared the Real IRA a terrorist group under U.S. law on Wednesday.