"We continue in this hour, on this day, to pursue diplomacy because it remains at this moment the best option, but we are actively engaging with allies and partners on alternatives," he said during a visit to Indonesia.

Blinken referred to a recent statement by European countries involved in the talks, which he said noted that "time is running out, that Iran is still not engaged in real negotiations".

"Unless there's swift progress... the Iran nuclear agreement will become an empty shell," Blinken said, referring to the statement.

Negotiations restarted on Thursday last week to try to revive the 2015 deal between Iran and world powers, which the United States withdrew from under Donald Trump in 2018.