Equatorial Guinea's exiled opposition leader, Severo Moto, has been arrested in Spain after allegedly trying to send illegal weapons to the oil-rich African nation.

The arrest was the latest twist in a tangled case that has implicated figures such as Mark Thatcher, the son of the former British Prime Minister, and Simon Mann, the Eton-educated mercenary, who is facing trial in Malabo for his alleged role in a failed 2004 coup attempt.

Mr Thatcher, who now lives on the Spanish Costa del Sol, was given a suspended jail sentence after he pleaded guilty to unwittingly financing the coup attempt and breaking the anti-mercenary laws of South Africa. The arrest of Mr Moto raises questions about whether a fresh coup attempt was under way.

According to Spanish court sources, he was arrested on Monday on the orders of a judge after weapons were found in the boot of a car in the port of Sagunto, near Valencia, on March 6.

Mr Moto has run a self-proclaimed government-in-opposition from Spain, where he has had political asylum since 1986. He was sentenced in absentia to 62 years in prison in Equatorial Guinea for his alleged role in the failed coup against President Teodoro Obiang Nguema.

His status as a political refugee was revoked by Spanish authorities in 2005 after they accused him of using the country as a base for several coup attempts against the Government in Equatorial Guinea. The Spanish Supreme Court overturned the ruling on appeal last month, stating that Mr Moto posed no danger to Spain.

Mr Moto has denied any role in the attempted overthrow of the Government. Critics have accused the Spanish Socialist Government of being too close to the regime of Mr Obiang, which is considered to have one of the worst human rights records in Africa. The former Spanish colony is the third-largest African oil producer.

Equatorial Guinea issued an international arrest warrant for Mr Thatcher last month, accusing him of being a prime instigator behind the plot to overthrow Mr Obiang on behalf of Mr Moto, in return for access to the oil wealth of the country.

Mr Thatcher has admitted to paying $275,000 (£128,000) to charter a helicopter used in the coup attempt. He claimed he thought that it would be used for commercial purposes.

The prosecution in Equatorial Guinea said that Mr Mann implicated Mr Thatcher in the plot. It said: “Thatcher knew all about the operation. If we can gather enough evidence we will start a case against him.”

Armengol Engonga, the deputy opposition leader in exile of Equatorial Guinea, urged caution yesterday over the arrest of Mr Moto.

“As long as we don't know what this accusation is based on and the nature of the charges, we cannot say anything,” he told the AFP news agency.

Mr Obiang has called parliamentary elections for May 4, about a year earlier than expected. The trial of Mr Mann, who was arrested four years ago, is expected to begin after the vote and could be embarrassing for Britain and Spain as he seeks to show he had official support for his alleged attempt to overthrow the Government.

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