By Barnaby Phillips BBC Southern Africa correspondent

Police in South Africa have closed a road linking the coastal provinces of Eastern Cape and KwaZulu Natal after a blast on a bridge in the early hours of Thursday morning.

There has been a series of bomb attacks in South Africa in recent weeks, and police say they have uncovered a plot by right-wing Afrikaners to overthrow the country's African National Congress (ANC) government.

Police have not yet linked this latest explosion to any particular group, but the ruling ANC has released a statement condemning what it calls "lunatics who are bent on terrorising the public".

Suspicion will inevitably fall on extreme right-wing Afrikaner groups.

Gathering evidence

One, calling itself the "Warriors of the Boer Nation", says it carried out a series of bombings in the black township of Soweto four weeks ago, which killed one person.

One person was killed in the Soweto attacks

There were no casualties in this latest explosion, which happened in the middle of the night.

By daybreak, a large contingent of police and emergency service workers had arrived at the scene.

Forensic experts were busy examining the damaged bridge and gathering evidence.

This year the South African police have arrested about 20 Afrikaners and charged them with plotting to overthrow the government, treason and terrorism.