By Michael Martina, Reuters

US Secretary of State Marco Rubio.

Iran and the United States have played down hopes for an imminent breakthrough in the three-month-old war on Monday, with US Secretary of State Marco Rubio saying there will either be a good agreement or Washington would deal with the country in "another way."

Rubio told reporters in New Delhi that the US would give diplomacy every chance to succeed before exploring "alternatives", after President Donald Trump said on Sunday he had told his representatives not to rush into any Iran deal.

There was a "pretty solid thing on the table in terms of their ability to open up the strait, get the strait open, enter into a very real, significant, time-limited negotiation on the nuclear matter, and hopefully we can pull it off," Rubio said.