US military officials actively sought ways to implement harsh interrogation techniques such as waterboarding used at Guantanamo Bay despite legal objections, a senior Democratic senator has said.

Carl Levin, the Senate Armed Services Committee chairman, told a hearing the US government had "twisted the law to create the appearance of legality".

A US congressional committee is investigating accusations that the Pentagon ignored guidelines about how to treat detainees in US custody.

The head of that committee says defense department officials encouraged military interrogators to use illegal practices like torture.

Al Jazeera's Monica Villamizar reports from Washington.