Armed Palestinians briefly seized the United Nations club in Gaza City early Sunday, throwing two explosive devices.
They officials said five armed men tied up the guard at the building before throwing the explosives. No one was hurt, they said.
The building was damaged by the blasts. Plaster from the ceiling littered the floor of the seaside building.
The UN club is known as the only place in Gaza City where alcohol is served, but it was closed when the attack took place after 2 a.m. (0000 GMT). Only foreigners are allowed inside.
One of the explosives damaged the bar of the seaside building and broke many of the liquor bottles.
A flag from the UN refugee agency UNRWA flies over the building. A UN security official, who refused to give his name, said the club has been in operation for 15 years, but this is the first time such an incident has happened.
Islamic fundamentalists object to sale and consumption of liquor, but it was not immediately known who the attackers were.