Syria's highest-ranking diplomat in London, Khaled al-Ayoubi, has defected, according to the UK Foreign Office.
Ayoubi "has told us that he is no longer willing to represent a regime that has committed such violent and oppressive acts against its own people," a Foreign Office statement said.
His decision "illustrates the revulsion and despair the regime's actions are provoking amongst Syrians from all walks of life, inside the country and abroad," the statement said.
The Foreign Office urged other members of the Syrian government to follow suit.
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Ayoubi was the most senior Syrian diplomat left in the UK, President Bashar al-Assad having recalled the ambassador in March.
The British government expelled the former chargé d'affaires, Ghassan Dalla, in May, The Telegraph reported at the time, leaving the Syrian embassy in London with a "skeleton staff" of just four diplomats.
Britain was one of several Western countries to expel Syrian diplomats over mass killings in Hama, which are alleged to have been carried out by pro-government militia.
Since then, several Syrian military officers and a handful of diplomats have quit voluntarily. The highest-profile defector, former ambassador to Iraq Nawaf Fares, has since joined the opposition and called publicly on Syrians to take up arms against the regime.
Last week, Agence France Presse reported that Syria's ambassador to the United Arab Emirates, Abdel Latif al-Dabbagh, had resigned, along with the Syrian chargé d'affaires in Cyprus, Lamia Hariri, to whom Dabbagh is married.
Confirming their defections, White House spokesman Jay Carney said the development showed that "senior officials around the Assad inner circle are fleeing the government because of the heinous actions taken by Assad against his own people, and the recognition that Assad's days are numbered."
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