U.N. Secretary-General Ban Ki-moon is urging the Democratic Republic of Congo's political leaders to “exercise restraint” after violence marred the last day of campaigning ahead of Monday's national elections.

In a statement Sunday, Mr. Ban called on Congolese politicians and their followers to respect election laws and use legal means to settle any disputes about the results. He also said the Congolese government has the main responsibility to ensure Monday's voting is peaceful.

President Joseph Kabila is seeking re-election against 10 rivals in a single-round vote, while more than 18,000 candidates compete for 500 seats in the national assembly.

Confrontations erupted Saturday between supporters of Mr. Kabila and his main rival Etienne Tshisekedi in the capital, Kinshasa, with police firing tear gas and live ammunition to disperse the crowds. Two people were killed and several others were injured.

Preparations for the election also were running behind schedule. Bad weather delayed the delivery of ballot materials to 60,000 polling stations spread across a large country with few paved roads. It was not clear if the ballots would reach polling stations in Congo's remote interior by Monday.

Mr. Kabila is expected to win a third term, partly because much of the opposition vote will be split among three candidates. He inherited power on the death of his father, Laurent, in 2001, and won the country's last presidential election in 2006.

Saturday's confrontations in Kinshasa began as tens of thousands of people, mostly Tshisekedi supporters, gathered on roads leading to the city's airport and at the airport itself ahead of the expected arrival of Mr. Tshisekedi and Mr. Kabila.

Followers of the rival candidates threw stones at each other at the airport and on the airport road, prompting police to intervene. Kinshasa authorities banned campaign rallies planned for later in the day to prevent further violence.

President Kabila canceled his rally, but Mr. Tshisekedi vowed to defy the ban and lead his supporters from the airport to a rally at Kinshasa's largest stadium. But, police blocked Mr. Tshisekedi and his entourage from leaving the airport for several hours and forced the convoy to break up, beating and dragging several people from their cars.

The United States, European Union and United Nations have expressed concern about election-related unrest and violence in Congo. The International Criminal Court has said it will prosecute any perpetrators of election-related crimes.