Keyholders of large stores in Londonderry were asked to return to their shops after an incendiary device partially exploded on Monday night.
A fire at a B&Q warehouse was started by an incendiary device
The Homebase store in the Waterside was evacuated about 2100 GMT but only minor damage was caused.
The store is in the Crescent Link area of the city where a fire broke out at a Carpetrite shop on Sunday.
Earlier, police confirmed a fire at the B&Q DIY store near Lisburn was started by an incendiary device.
More than 100 firefighters were involved in tackling the blaze at the warehouse in Sprucefield Retail Park on Sunday night.
There was extensive damage to the rug department and smoke damage to the rest of the property.
At one stage 20 fire engines attended the blaze, which took eight hours to bring under control.
Democratic Unionist Party MP for Lagan Valley, Jeffrey Donaldson, condemned the attack.
A blaze destroyed a large carpet shop in Londonderry
He said: "Those responsible have absolutely nothing to offer the people of this province and are only seeking to drag us backwards.
"In the run up to Christmas, this is a serious blow to the local economy."
Meanwhile, forensic tests after the blaze on Sunday morning at the Carpetrite store at the Crescent Link complex, have not established the cause.
The fire, which caused £100,000 of damage, was so fierce that it took 40 firefighters three hours to bring it under control.
Police said that a "detailed and thorough" examination was carried out and the cause of the fire is, as yet, "undetermined".
Inquiries are continuing.