US President Donald Trump's special envoy Steve Witkoff and his son-in-law Jared Kushner traveled to Oak Ridge National Laboratory in Tennessee on Thursday to consult with experts who could play a role in nuclear negotiations with Iran, a source familiar with the trip said on Friday.

The source, confirming an Axios report, did not provide additional details. President Donald Trump is adamant that any deal to end the war with Iran must include a provision that Tehran will not develop nuclear weapons.

Iran is believed to possess about 900 pounds of highly enriched uranium, which was in sites bombed by US planes a year ago.

Tehran has been determined to maintain the ability to enrich uranium and denies developing a weapon.