on Thursday that the copilot, identified by Israeli officials as an Omani citizen, had undergone  Islamist radical indoctrination  but provided no evidence to back the assertion.

Similarly, U.S. President Donald Trump told reporters that early information he's received suggests there are links between the attack and Tehran but did not elaborate.

Trump also said that if it is determined that Iranian agents were behind the attack, the United States will  hit them very hard. 

Israeli investigators are involved in the probe but the Emiratis are in the lead, according to an official who wasn't authorized to speak to the media and spoke on condition of anonymity. It's unclear if the attacker was part of a group, said the official, adding that there is currently no evidence of a link with Iran.

The FlyDubai flight plummeted to 15,000 feet

Details of the harrowing flight, which made an emergency landing in Tabuk, Saudi Arabia, continue to emerge.

Smit Machchhar, the wounded captain who has been hailed as one of the heroes of the flight, and the copilot were transferred on Thursday from Saudi Arabia to the UAE, the kingdom said.

Machchhar is recovering in an Abu Dhabi hospital. He spoke with Indian Prime Minister Narendra Modi in a televised video call Friday, describing the terror he faced after being attacked in the closed cockpit by his copilot.

 I had so many wounds. I had fallen down,  he said from the hospital, his head bandaged and breaking into sobs.  I was fighting for my life. At one point, I realized that if I didn't get up … then passengers would lose their lives. 

A wounded Machchhar still managed to open the cockpit door, allowing passengers to enter and restrain the attacker as the Boeing 737 - with 174 passengers and eight crew members - descended sharply.

For the passengers on board, most of them Israelis, the first signs of trouble came more than two hours into the flight when the aircraft suddenly dropped down to 16,600 feet - the sharpest drop in altitude recorded by data tracking platforms.

Seconds later, it ascended to 21,725 feet before soon dropping back to 15,000 feet, which it maintained until safely landing more than an hour later.

Soon after leveling off, the plane dispatched its first distress signal, Squawk 7700, a code for general emergency, while flying along the Saudi-Jordanian border. It then sent a second distress signal, 7500, for  unlawful interference,  indicating something more serious like a hijacking attempt or an attack. It lasted for nearly an hour.

About 15 minutes after the second distress call, the aircraft turned west, briefly entering Jordanian airspace, then made a 180-degree turn and headed southwest to Tabuk, where it eventually landed, nearly four hours after taking off from Dubai.

Possible implications for US-Iran war negotiations

Trump's suggestion that there could be an Iranian link adds a new layer of uncertainty to the on-and-off diplomatic efforts aimed at bringing an end to the seven-month war in Iran.

Iranian officials said Wednesday they received an official U.S. response to Tehran's latest proposal to end the conflict, which Trump had publicly rejected just days earlier. The officials did not say what the response contained and whether it was a rejection.

The U.S. is meanwhile dispatching roughly 9,000 more troops on ships to the Middle East, a U.S. official said Thursday - a move that could further complicate the political climate in the U.S., with looming midterm elections.

The ships include the USS Theodore Roosevelt carrier strike group, which recently deployed with the cruiser USS Chosin, and the USS Makin Island amphibious readiness group, which includes the USS John P. Murtha and USS Anchorage amphibious landing ships.

That could mean there would be three carriers in the region as early as the end of October, according to the U.S. official, who spoke on condition of anonymity to discuss military operations.

The move would bring the U.S. naval presence in the Middle East to an unusually high number of more than 20,000 sailors and Marines, as well as hundreds of aircraft. The Navy previously had three carrier strike groups in the Middle East in April for the first time since 2003.

Trump has threatened that a post-election escalation remains possible despite his initial promises to Americans of a campaign that would last a matter of weeks.

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Madhani reported from Jerusalem. AP writer Konstantin Toropin in Washington contributed reporting.