US President Donald Trump has warned that Iran would be “hit very hard” if it is found to be involved in an alleged attack on a Flydubai flight carrying mostly Israeli passengers to Israel.

Trump issued the warning on Thursday as the United Arab Emirates investigated whether the incident, which forced the aircraft to make an emergency landing in Saudi Arabia, was linked to terrorism.

Passengers reportedly helped overpower the co-pilot after he allegedly attacked the captain and attempted to take control of the aircraft. The passengers were later flown to Israel on a replacement flight.

Asked whether Iran was involved, Trump said, “I would say the answer, based on what I’m hearing, is yes, but we’re working on it right now.”

He added that Iran would be “hit very hard” if found responsible.

The warning came amid reports of increased US military deployments in the region, including additional Patriot missile batteries in Saudi Arabia and Qatar.

Saudi Arabia said the co-pilot was handed over to the UAE on Thursday after its preliminary investigation indicated that he had attacked the captain.

Israeli Prime Minister Benjamin Netanyahu identified the co-pilot as an Omani national and said he had undergone “Islamist radical indoctrination”, describing the incident as an attempted terrorist attack.

The UAE chief prosecutor said investigators would determine whether there was “terrorist activity or intent”.

Netanyahu credited the captain, Smit Machchhar, an Indian national, and passengers with preventing a possible disaster after the co-pilot allegedly stabbed him and attempted to crash the aircraft.

Passengers said the plane lost about 17,000 feet in altitude within a minute before they rushed to the cockpit to help regain control.

Flydubai said another crew member on board landed the aircraft safely and announced the suspension of flights to Israel pending the investigation.

Indian Prime Minister Narendra Modi described Machchhar as a “HERO”, while Israeli President Isaac Herzog said he would honour five passengers who helped overpower the co-pilot.