WASHINGTON - US State Department officials on Tuesday offered their most detailed description yet of the dramatic events in Benghazi that led to the death of a US ambassador, but they backed away from earlier assertions that the events were triggered by protests against an anti-Islam video.

The officials were briefing reporters on the eve of a congressional hearing into on the attack last month, which is expected to focus on security missteps by the department.

They described frantic and prolonged efforts to rescue Ambassador Christopher Stevens from a smoke-filled "safe haven" inside the U.S. diplomatic compound in Benghazi where he apparently died of asphyxiation.

Stevens' death and confusion over the attack has become the subject of fierce partisan debate in Washington in the final weeks before the US presidential election on November 6.

The State Department officials said agents crawled on their hands and knees through thick diesel smoke to try to find the missing envoy, who somehow was transported out of the compound to a local hospital.

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