They were responding to "a specific, imminent threat to Westerners," a week after the hostage siege at an Algerian gas field left scores of foreigners dead.  Wednesday, US Secretary of State Hillary Clinton testified to a House Committee on the murders of Ambassador Chris Stevens and three of his staff in Benghazi last September. DEBKAfile: The advisories apply in effect to nationals of the three nations employed in Libyan oil fields since most have accommodation in Benghazi.