Barack Obama: 'It's an unusual coalition'

US President Barack Obama has criticised a letter from Republican senators to Iran, accusing them of "interfering" in ongoing nuclear talks.

In an open letter 47 senators warn Iran's leaders that any deal on Tehran's nuclear programme could be revoked once President Obama leaves office.

Talks on Iran's nuclear programme are at a critical stage, with an outline agreement due on 31 March.

President Obama said he was confident he could implement any deal reached.