Thatcher, the son of former British Prime Minister Margaret Thatcher, will pay a $506,000 fine in a deal that lets him leave South Africa to rejoin his family in the United States. If he does not pay the fine, he faces a five-year prison sentence with a further four years suspended sentence, Judge Abe Motala said in the Cape High Court.

Thatcher admits that he paid for a military helicopter used by mercenaries in the alleged plot but maintains that he believed it was to be used as an air ambulance for humanitarian purposes, a person close to the family said.

Thatcher and his lawyers did not address a large crowd of journalists gathered outside the building as they arrived Thursday morning for the brief court appearance. A poster reading "Save me mummy" hung from a window across the street.

A spokesman for Lady Thatcher's office in London said late Wednesday: "She is very relieved that matters have now been settled and that the worry of these last few months is now over."

Thatcher, who has lived in South Africa since 1995, was arrested at his suburban Cape Town home on Aug. 25 and charged with violating this country's anti-mercenary laws.

He also faces charges in Equatorial Guinea, where 19 other defendants are already on trial in connection with an alleged plot last year to overthrow President Teodoro Obiang Nguema, who has ruled Africa's third-largest oil producer for the past 25 years. Officials there have said they will seek Thatcher's extradition from South Africa.

Equatorial Guinea alleges Thatcher and other mainly British financiers worked with the tiny country's opposition figures, scores of African mercenaries and six Armenian pilots in a takeover attempt foiled in March. Thatcher maintains he played no part in the alleged conspiracy.

The high court in South Africa ordered Thatcher to answer questions submitted by Equatorial Guinea under oath in November, but that appearance was postponed until Feb. 18 to give his lawyers a chance to appeal the ruling.

Thatcher's trial on charges of violating South Africa's Foreign Military Assistance Act had been postponed until April 8 for further investigation before he pleading guilty Thursday to a charge of attempted financing of a coup in West Africa.