US President Donald Trump warned on Thursday that Iran would be struck “very hard” if it is found to be behind the co-pilot who tried to crash an Israel-bound flydubai flight.

The co-pilot stabbed the captain during the flight, sending the jet into a plunge before passengers and crew subdued him. The plane made an emergency landing in Saudi Arabia.

Asked at the White House whether he had been briefed on an Iranian link, Trump said, “We’re working on it right now.” He added, “I would say the answer, based on what I’m hearing, is yes,” but offered no evidence for his suspicion.

However, two Israeli security officials told Reuters their initial assessment was that the co-pilot, identified as an Omani national, probably acted alone. They said Israel has found no evidence of Iranian involvement so far.

Prime Minister Benjamin Netanyahu said it was too early to draw conclusions, though he claimed the suspect showed signs of “Islamist extremism.”

The injured captain has been transferred to Abu Dhabi for treatment. Saudi Arabia has handed the suspected co-pilot to the UAE, where investigators are examining the motive and any possible link to terrorism.