Police in the Democratic Republic of Congo have fired tear gas at opposition protesters accusing the electoral commission of fraud.
Hundreds of protesters were stopped as they approached the commission's headquarters in the capital, Kinshasa.
Etienne Tshisekedi is due to stand against President Joseph Kabila in November polls.
His Union for Democracy and Social Progress claims some voter registration has been fraudulent.
Mr Tshisekedi has called for an audit of the electoral register.
Police chief Charles Bisengimana said two demonstrators were arrested and two police officers were injured.
The UDPS said there had been injuries and arrests, denouncing the "violent repression of a non-violent protest".
Mr Kabila became president in 2001 and was re-elected in 2006, in the country's first democratic elections.