Managua (AFP) - More than 20 people have been killed in a clashes between Nicaraguan police and demonstrators in a wave of protests over pension reform, a local human rights body said Sunday.

The Nicaraguan Center for Human Rights said it was still trying to verify figures, but that at least 20 people had been killed since protests erupted in the central American country on Wednesday over plans by President Daniel Ortega to reform the nation's pension system.

"We are dealing with more than 20 dead, but we are verifying because there is a lot of misinformation, the situation is really serious and beyond our possibilities to confirm," the Center's director Vilma Nunez told AFP.

On Friday, the government put the number of people killed in two days of protests in the capital Managua and other cities at 10, the last official figure.

The streets of Managua were rubble-strewn early Saturday after a night of clashes between police and demonstrators.

Nicabus, an international bus line with links to Costa Rica and Honduras, said it has been forced to suspend services due to the violence.

Protest groups on Sunday announced a march to the Polytechnic University in the capital where hundreds of students have been holed up since Thursday.

In a bid to calm the protests -- the biggest of his 11-year presidency -- Ortega agreed Saturday to speak with the private sector about social security reforms, only to be rebuffed by Nicaragua's top private-sector business union.

They said there could be no dialogue unless the government "immediately ceases police repression."

On Saturday local media reported that journalist Miguel Angel Gahona was shot dead by a suspected sniper in the city of Bluefields, on Nicaragua's Caribbean coast.

Journalists have reportedly faced attacks, been temporarily detained and had their work equipment stolen since the start of the protests. Meanwhile, four independent television outlets were taken off air on Thursday, although only one currently remains closed.