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

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.

A day earlier, Trump wrote on Truth Social that the US blockade on Iranian ships in the Strait of Hormuz would "remain in full force and effect until an agreement is reached, certified, and signed".

"Both sides must take their time and get it right," he added.