British police said today they had arrested a Libyan man over his suspected role in the murder of policewoman Yvonne Fletcher, who was shot dead outside the Libyan embassy in London in 1984.

Fletcher, who was 25, was hit by a shot fired from the embassy during a demonstration by Libyan dissidents against Muammar Gaddafi, who then ruled the North African country.

The shooting triggered an 11-day siege of the building by London's Metropolitan Police, the deportation of 30 Libyans in the embassy and the severing of diplomatic ties between London and Tripoli.

"This is the first significant arrest in this investigation" Richard Walton, who heads London police's counter-terrorism command, told reporters.

Walton said a man in his 50s had been arrested in southeast England on conspiracy to murder and money laundering offences. A woman in her 40s and a man in his 30s, also Libyan, were also arrested for money laundering.

The arrest of the murder suspect comes as a result of new information obtained since the fall of Gaddafi in 2011, with London officers having made seven visits to Libya since then.

Police believe there was a deliberate conspiracy to murder police officers and Gaddafi opponents, and that those involved in a pro-Gaddafi counter-demonstration outside the embassy were receiving instructions from within the building.

Police said they would launch their biggest ever Facebook campaign as part of a global appeal for more information. They are also offering a 50,000-pound ($76,000) reward for information leading to the capture and prosecution of those involved.

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