But a channel for diplomacy remains open, with Iran taking a "far different tone" in private discussions with Trump's special envoy Steve Witkoff, said Press Secretary Karoline Leavitt.

"One thing President Trump is very good at is always keeping all of his options on the table. And air strikes would be one of the many, many options that are on the table for the commander in chief," Leavitt told reporters outside the West Wing.

Leavitt added that "diplomacy is always the first option for the president."

"What you're hearing publicly from the Iranian regime is quite different from the messages the administration is receiving privately, and I think the president has an interest in exploring those messages," Leavitt added.

Iran's foreign ministry said earlier Monday that a channel of communication was open between its top diplomat Abbas Araghchi and Trump's special envoy, despite a lack of diplomatic relations.

Trump said on Sunday that the US military was considering "very strong options" against Iran, saying it "looks like" Tehran had crossed his previously stated red line of protesters being killed.

He said Iran's leaders had reached out for a meeting but "we may have to act before a meeting."

Rights groups have reported a growing death toll, with information continuing to trickle out of Iran despite a days-long internet shutdown.

Leavitt appeared to confirm there had been deaths.

"He certainly doesn't want to see people being killed in the streets of Tehran, and unfortunately that's something we're seeing right now," Leavitt said.