Security forces patrolled the streets in the Democratic Republic of Congo's capital Friday, after riot police clashed with supporters of opposition parties.

Witnesses say the violence occurred as the opposition supporters marched down a main Kinshasa boulevard to the United Nations mission in Congo.

Heavily armed police fired tear gas at the demonstrators, beat them with batons and arrested more than 40 people.

The march organizers say they were heading to the U.N. mission to present a memo outlining their concerns about upcoming elections.  U.N. officials expressed regret about the violence, noting they were ready to receive the party's memo.

Friday's violence comes one day after President Joseph Kabila approved a new electoral law, clearing the way for long-awaited elections set for June 18.

Officials can now begin to register candidates, print ballot papers for some 25 million voters, and begin distributing them around the country.

The new law did not set a date for a second round of elections, but observers believe it will happen after a June 30 deadline set in the 2002 peace deal that ended Congo's five-year war.