Egypt on Sunday deployed a submarine to hunt for the black box flight recorders of the EgyptAir plane that crashed in the Mediterranean Sea with 66 people on board, President Abdel Fattah al-Sisi said, according to Reuters.

International air and naval teams discovered debris of the plane Friday, 180 miles (290 kilometers) north of Alexandria. Among the wreckage were personal belongings of passengers and crew. 

But the ships scouring the sea north of Alexandria are still trying to locate the recorders which could shed light on the cause of Thursday’s crash.

Sisi said that underwater equipment from Egypt’s offshore oil industry was being brought in to help the search.

“They have a submarine that can reach 3,000 meters under water,” he said in a televised speech and quoted by Reuters. “It moved today in the direction of the plane crash site because we are working hard to salvage the black boxes.”

French investigators said on Saturday that the plane sent a series of warnings indicating that smoke had been detected on board shortly before it disappeared off radar screens.

The signals did not indicate what caused the smoke or fire, and aviation experts have not ruled out either deliberate sabotage or a technical fault, but they offered early clues as to what unfolded in the moments before the crash.

Meanwhile, reports Saturday said that political vandals threatened the doomed plane before the flight, writing in Arabic “we will bring this plane down” on the plane’s underbelly. Three EgyptAir employees anonymously confirmed the incident, though they stressed that it was political, not terrorism-related.

“Until now all scenarios are possible,” Sisi said Sunday in his first public remarks on the crash. “So please, it is very important that we do not talk and say there is a specific scenario.”

The crash was the third blow since October to hit Egypt’s travel industry, still reeling from political unrest following the 2011 uprising that ousted Hosni Mubarak.

A suspected Islamic State bombing brought down a Russian airliner after it took off from Sharm al-Sheikh airport in late October, killing all 224 people on board, and an EgyptAir plane was hijacked in March by a man wearing a fake suicide belt.

Islamic State claimed responsibility for the Sharm al-Sheikh bombing within hours, noted Reuters, but a purported statement from the group’s spokesman Abu Muhammad al-Adnani, distributed on Saturday, made no mention of the crash.