The US delegation would be led by William Burns, the State Department's undersecretary for political affairs.

'We hope that the six (countries) can really lay out in a very stark fashion the choices they have, and we're going to take this opportunity to do that,' Kelly said.

US Energy Secretary Steven Chu earlier said the US was keeping open the option of introducing more sanctions against Iran. The UN Security Council has already imposed three rounds of sanctions aimed at convincing Tehran to halt its uranium enrichment programme.

The West believes Iran has designs on a nuclear weapons programme. Tehran insists it only plans to develop civilian nuclear energy.