text:  The UN Human Rights Office has said it's looking into reports of a mass grave of suspected migrants in the desert along the Libya-Tunisia border. The High Commissioner, Volker Turk, said the responsibility for investigating fell squarely on Libya. Libby Capellan reports. Mr Turk has urged the two countries to investigate swiftly the alleged crimes in line with their responsibilities, adding the relatives of the victims had every right to know the truth.