Police in Democratic Republic of Congo have fired tear gas at opposition supporters in Kinshasa on the first day of campaigning for landmark elections.
President Kabila is expected to win his first elections
Veteran opposition leader Etienne Tshisekedi is boycotting the polls and his supporters held a protest march.
The elections follow the official end of DR Congo's five-year war in 2003.
However violence continues - 11 people have been killed in clashes between the Congolese army and a religious group in the western port city of Matadi.
Deputy UN spokesman in DR Congo Jean-Tobie Okala told the BBC that the Bundu dia Kongo religious group was holding a march in Matadi during which a soldier was killed and five more seriously wounded.
DR CONGO'S ELECTIONS
33 presidential candidates
8,650 parliamentary candidates
500 parliamentary seats
267 registered political parties
25m registered voters
Other soldiers then opened fire on the thousands of demonstrators, killing 10.
Reuters news agency reports that the Bundu dia Kongo seeks the restoration of the ancient Kongo Kingdom, which includes parts of Angola, Congo, DR Congo and Gabon.
But Mr Okala stressed that the deaths had nothing to do with the 30 July elections.
The UN, and its 17,000 peacekeepers, are helping to organise what are hoped will be DR Congo's first democratic polls in 45 years.
After years of conflict and misrule, holding the elections will be a major challenge - there are no roads or railways linking one side of the country to the other.
Thirty-two candidates are opposing Mr Kabila in the first round of the presidential vote, including two vice-presidents and former rebel leaders.
Friday 30 June was the original date for the end of the transitional period following the end of the war but the elections have been postponed several times and so the deadline has been missed.
Opposition supporters say this means the power-sharing government led by Mr Kabila should resign.
"Today is the end of the transition. Today everything comes to an end," said Pierre Luabeya, a supporter of Mr Tshisekedi's Union for Democracy and Social Progress (UDPS) party.
Mr Tshisekedi wants voter registration to be reopened, after he initially called on his supporters to boycott the process.
UDPS activists tore down some of the new posters put up by the parties taking part in the elections, leading to clashes between rival groups.
Friday is also a public holiday to make 46 years of independence from Belgium but correspondents say many residents of the capital stayed at home in case of serious violence.
There is a heavy deployment of police and UN peacekeepers on the streets.
On Friday the UN Security Council voted to extend the mandate of more than 1,100 extra UN peacekeeping personnel in DR Congo until 30 September to aid successful elections. They include a 300-strong infantry battalion in Katanga province.
Appeal for restraint
Some of the parties contesting the poll met in Kinshasa to discuss security and media access but Mr Kabila's party was not among them.
The BBC's Arnaud Zajtman in Kinshasa says President Kabila's campaigns have been broadcast live on state television across the country, but other candidates have struggled for media access.
Most parties have been campaigning for several months
The UN has appealed for political parties to avoid inflammatory statements, and to refrain from inciting ethnic hatred.
The elections are intended to end a post-war transitional period, with the government made up of various warring factions.
But armed men still roam parts of eastern DR Congo, three years after the official end of the five-year conflict.
The last free democratic election was at independence from Belgium in 1960.