Amateur video has been uploaded on to a social media website showing members of a Libyan militia in what is thought to be the abandoned US embassy in Tripoli
The diplomatic facility appears to be an annex of the main complex which the United States evacuated its staff from last month.
Its takeover is a symbolic blow to Washington over its policy towards Libya, which is teetering towards becoming a failed state just three years after the ousting of Muammar Gaddafi
Libya continues to be rocked by factional violence – on Sunday Islamist militias said they had consolidated their hold on Tripoli and its international airport, driving out other militias to the outskirts of the capital following a week long battle.
In Libya’s second city of Benghazi heavy clashes left 10 people dead on Saturday.