Nigeria’s security forces have reportedly shot dead demonstrators protesting against police brutality in Lagos, according to several witnesses, as authorities imposed a curfew and promised an investigation.

Soldiers fired at the protesters who had gathered in the Lekki district of Nigeria’s largest city in defiance of an indefinite curfew imposed hours earlier by the authorities.

Hundreds of people were at the site at the time of the shooting, which witnesses said took place around 7pm local time (18:00 GMT).

The army denies the reports. Officials have promised an investigation. An indefinite 24-hour curfew has been imposed on Lagos and other regions.