BEIRUT, Dec 18 (Reuters) - Lebanese security forces have arrested a Lebanese taxi driver suspected of killing Rebecca Dykes, a British woman who worked at the British embassy in Beirut and was found dead on Saturday, a security source said.

The motive was purely criminal, not political, preliminary investigations showed, the security source said. Lebanese state media also reported a taxi driver had been arrested, citing a security source.

(Reporting By Laila Bassam and Angus McDowall; editing by John Stonestreet) ((angus.mcdowall@thomsonreuters.com; Reuters Messaging: angus.mcdowall.thomsonreuters.com@reuters.net))