A protest against police violence in the Nigerian capital, Abuja, has been attacked by unidentified men wielding machetes.

Witnesses said several hundred demonstrators were gathered in the city centre on Wednesday when the attack took place.

One protester said some of the assailants were later detained and handed over to the authorities.

Demonstrations have taken place in cities across Nigeria in the past week. The unrest has continued despite the dissolution of a controversial police unit - the Special Anti-Robbery Squad, also known as Sars.

The protesters have vowed to remain on the streets.