An explosion hit a McDonald's restaurant in the city center on Sunday, injuring at least six people, officials said.

The explosion blew out windows at the restaurant and partially destroyed the ceiling, said Irina Andriyanova, spokeswoman for the Emergency Situations Ministry.

She said six people were wounded, including four who were hospitalized with various injuries, including concussions and cuts from flying glass.

Ekho Moskvy radio, citing eyewitnesses, said the blast went off in the handbag a restaurant patron.

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Officials did not say whether they believed the explosion was related to terrorism or a criminal act. McDonald's restaurants have been targets of both criminal gang disputes and terrorist attacks in Russia in the past.

In 2002, a car bombing at a McDonald's restaurant in Moscow killed one person and injured eight. Several Chechen men were convicted in the blast, which prosecutors said was part of a series of terrorist attacks planned by Chechen rebels.

In 1998, a small bomb exploded at a McDonald's under construction in another part of St. Petersburg.