The United States and Iran have begun a third round of nuclear talks, entering what experts describe as a more difficult phase of technical negotiations this weekend as Washington lays out its conditions.

MUSCAT (Reuters) -Top Iranian and U.S. negotiators began a new round of indirect talks on Saturday to hammer out a deal curbing Tehran's nuclear programme, while U.S. President Donald Trump signalled confidence in clinching a new pact that would block Iran's path to a nuclear bomb.