Britain has asked airlines worldwide to block American Edward Snowden, who leaked details of US government telephone and internet surveillance programs, from boarding any plane headed for the United Kingdom, the Associated Press reported on Friday.The Associated Press, in a report out of Bangkok, said British officials confirmed a travel alert from its Home Office issued on Monday telling airlines to deny Snowden from boarding because "the individual is highly likely to be refused entry to the UK."Various airlines in Thailand, Malaysia and Singapore confirmed the alert, according to the AP, which said it learned of the British letter to airlines from a photograph of the request seen at an airport in Thailand.