Belfast city centre has been sealed off as experts examine a fire bomb believed to have ignited at a shop in the busy shopping district, just a few hundred metres from the site of a blast on Friday night.
Christmas party goers were forced to evacuate busy bars and restaurants on Friday, after a sports bag with a small explosive inside ignited on the pavement in the city's Cathedral Quarter.
"We are advising city centre businesses to check their premises for any suspicious objects," a police spokesperson said.
The escalation by extremists opposed to the peace process has also included posting letter bombs to senior police commanders and Northern Ireland Secretary Theresa Villiers.
Police have stepped up their presence since masked men forced a terrified driver to bring a bomb into a Belfast city centre car park in November.