Thirteen people, including one soldier, were killed Friday in political violence as campaigning began for Congo's first competitive elections in decades, a human rights worker said.

Demonstrators in the eastern city of Matadi attacked and killed the soldier before troops retaliated firing on the crowd, killing 12 civilians in the crowd, said Christian Malidini, of Congo's Association of Human Rights Defenders.

Malidini, who spoke by telephone from the city 400 kilometers (250 miles) southeast of the capital, Kinshasa, had no further details. Officials in the city couldn't immediately be reached for comment.

The deaths were the first reported in the campaign ahead of a scheduled July 30 vote.

Nearly three dozen candidates are vying for the presidency and thousands for parliament in Congo's first multiparty elections in 40 years, balloting for a government to take over from a transitional administration arranged in the wake of a 1998-2003 civil war that drew armies from neighboring countries into the vast central African nation.

Fearing political clashes, the governor of the province that includes Kinshasa announced on state radio late Thursday that all marches and demonstrations were banned in the city.

But groups of young men still took to otherwise deserted streets Friday, seeking to assemble to voice support for their candidates. Riot police swinging batons and firing weapons into the sky scattered the crowds. Most shops, banks and schools stayed closed.

Logistical and political problems had led to repeated delays in the voting. Congo's elections were meant to be held in 2005, but have now been set for the end of the month -- even though the mandate expired Friday for the transitional government.

Leading opponents to President Joseph Kabila say his national unity government was illegitimate as of Friday, though the international community disagrees. The official Friday launch of campaigning coincided with the day marking Congo's independence from Belgium in 1960 -- a potentially combustible mix of history and politics in a country without a tradition of peaceful politics.

The country's 62 million people hope a democratically elected leadership can bring long-term peace to Congo after decades of corrupt rule and the war whose aftershocks continue to kill.

The presidential race has 33 candidates and 9,000 are running for the 600-plus seats in the National Assembly and Senate.

Kabila is a favorite in the presidential field, but few believe he can win an outright majority in the first round. A second round of the two top vote-getters would be held within weeks of the initial ballot's results if the first-round does not yield a clear winner.

Some 17,500 U.N. troops who are the rank and file of the United Nations' largest peacekeeping operation are overseeing the vote.

Hundreds of European Union troops are expected to arrive in Kinshasa in the coming weeks to beef up security.

Eastern Congo, where U.N. peacekeepers and Congolese troops are battling militants, remains restive after the official end of the war.

Aid groups estimate violence since 1998 has left some 4 million Congolese dead since 1998, mostly through strife-related disease or hunger. Suffering from extreme privation, an estimated 1,000 Congolese still die needless deaths daily, making Congo site of one of the world's worst humanitarian crises.