South African police have carried out a series of raids across the country as part of a wide-ranging investigation into an alleged right-wing plot to topple the government.

Police spokesperson Sally de Beer told BBC News Online that a number of arrests had been made, mostly for unlawful possession of firearms.

"The operation began at 0500 [local time] in all nine provinces, and by the end of the day we will have visited 94 farms and houses," she said.

She said the police are expecting those arrested to assist them in their broader investigation into the plot to overthrow the government, she said.

Bombs

Friday's raids come in the wake of a series of 13 small bomb blasts that began last month.

The most recent attack was on a bridge linking the coastal provinces of Eastern Cape and KwaZulu/Natal in the early hours of Thursday morning.

Mad right-wingers who threaten the peace will come to rue the day they were born

Minister of Intelligence Lindi Sisulu

One person died and three others were injured in the attacks, which also targeted railway lines, a police station, an airport and a Buddhist temple.

The government is blaming white right-wing extremists for the bombings.

About 20 right-wingers have been charged this year with plotting to overthrow the government, treason and terrorism.

Most of the accused are thought to be members of the Boeremag, or Farmers' Force, a group which was unheard of until the bombings began.

The "Warriors of the Farmers' Nation", a group which police suspect is a front for the Boeremag, has admitted carrying out the recent bomb attacks.

On Friday afternoon, the South African Press Association said it had received an e-mail warning that the group was planning more violence, according to the Associated Press.

The message said the Boeremag warned of further violence over the Christmas season, and that the bomb attacks were the beginning of the end for the government and the "oppression of the Boer nation".

Killer's wife 'arrested'

There are reports that one of the people arrested in Friday's raids is Gaye Derby-Lewis, whose husband Clive was convicted of the 1993 killing of Chris Hani, the popular leader of the South African Communist Party.

One person was killed in the Soweto attacks

Clive Derby-Lewis and Polish immigrant Janus Walusz are currently serving life sentences for Hani's murder.

Ms De Beer confirmed that a 63-year-old woman had been arrested for illegally possessing a firearm, but refused to say whether it was Mrs Derby-Lewis.

Hani's murder caused widespread unrest in South Africa, leaving more than 70 people dead in the ensuing violence.

Campaign

Friday's crackdown has gained widespread support from both opposition groups and members of the public, and the government is determined to stamp out the violence.

Minister of Intelligence Lindi Sisulu said: "Mad right-wingers who threaten the peace will come to rue the day they were born."

Fears of violence by right-wing groups with military connections haunted the elections which brought the first black-led government to power in 1994.

Since then, apart from a few isolated incidents, the threat had largely thought to have disappeared.

But then in September a group of well-educated white Afrikaners appeared in court charged with plotting to attack military bases with the aim of establishing an Afrikaner homeland.

The government says that extreme right-wingers would have little chance of successfully overthrowing the government.

But analysts say they are still capable of creating a considerable amount of disorder and destruction.