Three people were killed and two were seriously injured in a bomb explosion outside a downtown pizzeria, police said Monday.

The explosion occurred after two men entered the crowded pizzeria Sunday night and threatened to blow it up unless the owner gave them $13,000, police sources said.

A police officer, who was in the pizzeria at the time, managed to get the two men outside, but the bomb went off as the officer struggled to wrest it away. The officer and both assailants were killed.

It was the latest in a series of bomb attacks and shootouts attributed to Bulgaria’s growing underworld, which has mushroomed since the collapse of communism in 1989.