A top member of staff at the US Senate has said that a multi-million-dollar package to help Mexico fight drugs would be agreed by mid-June, but warned that the final version would contain strong conditions on human rights.

“We want to help Mexico, but the Congress is not going to turn over hundreds of millions of dollars with-out strings attached,” Tim Rieser, adviser to Senator Patrick Leahy, who chairs the appropriations subcommittee that funds US foreign aid programmes, told the Financial Times.