Speaking to reporters, Trump declined to spell out specific actions if negotiations collapse, but signalled a tough response.

“I don’t want to comment on that, but it won’t be pleasant for them,” he said, adding that hostilities had paused for now.

He pointed to existing pressure measures, saying Iran was already facing a blockade and had been largely cut off from business activity.

Trump also claimed that Iran’s military capabilities had been significantly degraded.

The US president reaffirmed Washington’s long-standing position on Iran’s nuclear programme, insisting that Tehran would not be permitted to acquire nuclear weapons.

“If they don’t agree, there is no deal… There will never be a deal,” he said, adding, “we are going to get the dust back; either we will get it back from them, or we will take it.”