Edward Snowden says he has offered to return to the United States and go to jail for leaking details of National Security Agency programmes to intercept electronic communications data on a vast scale.

The former NSA contractor flew to Moscow two years ago, and faces US charges that could land him in prison for up to 30 years.

Mr Snowden said he had "volunteered to go to prison with the government many times", but had not received a formal plea-deal offer.

He added: "So far they've said they won't torture me, which is a start, I think. But we haven't gotten much further than that."

In an interview with the BBC, Mr Snowden said he and his lawyers were waiting for US officials "to call us back".