COPENHAGEN, Denmark (AP) - At least three people were seriously injured Saturday when mounted riot police charged demonstrators in southern Sweden, authorities said.

Police spokeswoman Ewa-Gun Westford said officers on horseback chased rock-throwing demonstrators who were "causing violent riots" in Malmo, Sweden's third-largest city. Swedish media published photos of people on the ground as police horses raced over them down a street.

Approximately 1,000 people had gathered in Malmo to protest an election rally by a far-right group, the Party of the Swedes, ahead of the country's Sept. 14 parliamentary vote. Those injured were protesters.

Westford said a fourth person was slightly injured after being hit by a police van.

"It goes without saying that we are not happy with what happened today," Westford said.

Six people were detained for violence, public disturbance or wearing masks. It was not immediately clear whether they would be charged.