CAIRO—A leading Sudanese opposition figure says riot police have fired tear gas to stop demonstrators marching in several districts of the capital in the sixth day of protests against the regime.

Saata Ahmed al-Haj, who is head of the Sudanese Commission for Defense of Freedoms and Rights, says that protesters took to the streets after Friday prayers in and outside Khartoum.

He described a "cloud of tear gas" and said many arrests were made.

A government austerity plan slashing subsidies and doubling the price of fuel and food set off the protests. President Omar al-Bashir has said the measures are necessary to pay for his country's conflict with South Sudan and to replace lost oil revenues.