VIENNA - US Secretary of State John Kerry warned Monday it was too soon to tell if a nuclear deal with Iran is possible as he awaited the return of Iran's foreign minister from consultations in Tehran.

"We're just working and it's too early to make any judgements," Kerry told reporters in Vienna following a weekend of intense talks with counterparts from five other major powers and Iran.

In a possible sign meanwhile of progress, Russian Foreign Minister Sergei Lavrov said that he would arrive on Tuesday, coinciding with the expected return of his Iranian opposite number Mohammad Javad Zarif.

French Foreign Minister Laurent Fabius, speaking in New York, said he would be back in Vienna this week. It was unclear when his British, German or Chinese counterparts might follow suit.

Over the weekend officials from both sides made clear that their Tuesday deadline to nail down a deal was highly unlikely to be met, although they said they would only extend by several days.

Zarif flew back home on Sunday night, as did many of the other ministers.(AFP)