WASHINGTON (Reuters) - It is too soon to say whether Iran has returned to nuclear talks with a more constructive approach, the U.S. State Department said on Monday, after Iran's top nuclear negotiator said progress had been made.

       State Department deputy spokeswoman Jalina Porter made the comment during a briefing call with reporters.

       Iran's top nuclear negotiator, Ali Bagheri Kani, said over the weekend that good progress had been made in nuclear talks with world powers in Vienna that could quickly pave the way for serious negotiations.

       (Reporting by Daphne Psaledakis and Michael Martina; Editing by Chris Reese)