Riot police moved in to disperse protesters throwing stones in Peshawar in North-West Frontier Province.

Nationalists demanding greater political and economic rights also took to the streets in the restive south-west province of Balochistan.

Activists say ethnic groups in smaller provinces do not have equal rights.

Buses torched

Supporters of the Pakistan Oppressed Nations Movement (PONM) disrupted normal life in Balochistan, Sindh and North-West Frontier Province.

The shutdown was most effective in Peshawar and in Quetta, capital of Balochistan.

Hundreds of supporters of the regional and nationalist groups stayed on the streets of cities in Balochistan during the day to ensure a shutdown.

Reports from the interior of Sindh said businesses in most of the cities there were also closed and there was also a partial strike in Karachi, with shops shut in the suburbs and most public transport off the roads.

A government official said transport companies pulled buses off the roads because of overnight violence during which several vehicles were set on fire.

Three more buses were torched on Thursday morning.

In Peshawar, PONM supporters took to the streets on Thursday morning, throwing stones at passing vehicles and shops that had opened.

Police detained an opposition senator, Raza Ahmed Raza, and dozens of others.

Outlets of the Subway food chain and Honda cars were damaged.

Constitution

There were also reports of sporadic clashes in some parts of Balochistan, but officials say by and large the situation remained under control.

PONM is an alliance of several groups that aspire for greater rights for smaller provinces.

The alliance accuses the bigger province, Punjab, which has largely ignored the strike call, and the federal government of denying people rights in other areas.

They say that people in smaller provinces are not given their due share of jobs.

Its main demand is for a new national constitution to ensure equal rights.

The BBC's Zaffar Abbas in Islamabad says that recently the alliance has been rallying around armed Baloch nationalists, who in their campaign for greater rights have started what is effectively a mini-insurgency by targeting government installations in Balochistan.

Eight soldiers and dozens of local died in clashes at Dera Bugti last month.