At least 42 people have been killed in three days of protests in Democratic Republic of Congo over a proposed legal reform the opposition says would keep President Joseph Kabila in power for years.

Paul Nsapu, secretary general for Africa of the International Federation for Human Rights (FIDH), said most of the victims had been killed by government security forces as they took part in political protests.

The government, which says only 15 people have been killed, said most of the victims were shot by private security guards while looting.

"For the most part these people were killed while they were advancing to protest," Mr Nsapu said, adding that more than 100 people had been injured. "We don't expect the government to act in the same way as a rebel group."

In a third day of protests, police fired teargas at demonstrators at the university campus in the riverside capital Kinshasa,. Clashes also took place in three other areas of the teeming riverside capital,.

In the central neighbourhood of Matete, a witness reported security forces firing live rounds at protesters, who had erected barricades of burning tyres in the streets and responded by hurling rocks.