Police say there has been a small explosion in central Belfast, an attack that comes amid a spike in Irish republican activity.

The Police Service of Northern Ireland said Friday's explosion followed a telephoned bomb warning, a hallmark of Irish Republican Army attacks. The area was thronged with shoppers, but no injuries were reported.

Observers have warned that IRA splinter groups opposed to the outlawed group's 1997 cease-fire have increased their bombing efforts in the run-up to Christmas, a holiday that Irish republican extremists long have targeted in hopes of harming Northern Ireland's economy.

Last month the group failed to set off a car bomb underneath a shopping center — the first such attack in a decade.