U.S. Secretary of State Marco Rubio said in an interview aired on Monday (April 27) that Iran is using its threat to disrupt shipping through the Strait of Hormuz as an “economic nuclear weapon,” and that Tehran is trying to pressure the world while delaying talks on its nuclear programme.

Speaking to Fox News Channel’s Trey Yingst, Rubio said the nuclear issue remains the core driver of U.S. policy toward Iran and that pressure on the regime is already intense. “The nuclear question is the reason why we're in this in the first place", said Rubio.

The nuclear dispute between the U.S. and Iran has been a longstanding issue, with U.S. President Donald Trump having withdrawn from the 2015 Iran nuclear deal and threatened military strikes against Iran's nuclear program.

Trump is unhappy with the latest Iranian proposal on resolving the two-month war, a U.S. official said, dampening hopes for a resolution to the conflict that has disrupted energy supplies, fueled inflation, and killed thousands.

Iran's latest proposal would set aside discussion of Iran's nuclear program until the war is ended and disputes over shipping from the Gulf are resolved.

That is unlikely to satisfy the U.S., which says nuclear issues must be dealt with from the outset, and Trump was unhappy with Iran's proposal for that reason, a U.S. official briefed on the president's Monday (April 27) meeting with his advisers said, speaking on condition of anonymity.