THESSALONIKI, Greece (AP) — A month after squeezing into a rubber boat to cross a frigid river on the Greek-Turkish border, Syrian refugee Mohammad al Jarad sat in a chartered private jet leaving a small Greek airport for France.

The travel upgrade was the latest ploy by international smuggling gangs, which are exploiting rules meant to ease travel within Europe to spirit out well-paying migrants trapped in Greece by stringent land and sea border controls.

Greek police say 1,672 migrants were caught last year trying to get out of the country on regular flights using fake identity papers from all over the world, with most of the documents made in Greece itself. That's a large increase from 2016, and is considered so serious that German authorities launched checks on all flights arriving from Greece starting last November.

Greek police have now stepped up local airport ID controls, are training airline employees to detect fake papers and have sent officers to assist their colleagues in German airports.

The loophole being exploited by smugglers is looser identity checks for people flying within Europe's passport control-free region, the 26-country Schengen Area. Greece is a Schengen member, but has no land borders with other countries in the area.

"Traffickers try to take advantage of the Schengen Area regime ... where only airline employees carry out checks at boarding gates," said Lieutenant-General Zaharoula Tsirigoti, a top Greek police official responsible for border controls. "But we always have police carrying out checks at the gates for most Schengen countries. ... in most cases (the migrants) are stopped."

That's how al Jarad, from Syria's Daraa area, was caught just as he thought he had made it. He boarded the jet on Jan. 19 at the northern airport of Kozani with four other Syrians and a Kuwaiti, carrying a counterfeit Argentine passport.

Following Schengen regulations, nobody in Kozani checked their papers in depth against any database that would have detected stolen or forged documents, beyond seeing whether their stated identities matched the names on the plane tickets. But all 6 were detained by police in Thessaloniki airport, where the plane stopped to refuel.

An arresting officer testifying at the migrants' trial in Thessaloniki said police had special orders to check private flights for illegal migrants.

"We were really impressed that they chartered a small private aircraft from Egypt," Tsirigoti told The Associated Press. "It was the first — and only so far — incident of the kind. I believe it was a pilot run by traffickers who wanted to see if it would work."

Al Jarad said his group had agreed to pay smugglers 4,000-5,000 euros ($4,943 to $6,179) each to reach France. He had then intended to move to Britain, where his two brothers live, and bring over his wife and four young children. The payment for the chartered plane had been made by a member of the smuggling gang in Britain.

"They gave us passports, Mexican, Brazilian, Argentine," al Jarad said.

He spoke to the AP during a break in the trial, which ended with all six migrants receiving a three-month prison sentence, suspended for three years. Al Jarad had earlier paid other smugglers 1,700 euros ($2,100) to cross the Evros River into Greece and be driven to Athens — in addition to the $1,000 he spent to reach Turkey from Syria.

While expensive, the flight option is attractive, as it seems to offer a relatively high chance of success.

The land route, followed by a million people in 2015, has been blocked by a series of fences built along Balkan borders. And transport by sea from Greece to fellow Schengen member Italy is less appealing because of lengthier travel times, extra identity checks on the ship and the long next travel leg from Italy to migrants' final destinations.

Greece has a thriving illegal industry that churns out counterfeit passports and identity papers. In February, police in Athens working with Europol confiscated nearly 1,000 fake or stolen ID or travel documents — many imported from France and other countries. All were destined for migrants seeking to leave Greece. Eleven arrests were made.

Police in November closed down four workshops in Athens that allegedly delivered high-quality forgeries to clients within hours of receiving the order.

Another migrant caught trying to fly out with a forged passport is Firas Aassim, 23, a member of Iraq's persecuted Yazidi minority. He reached Greece in 2016, got to Serbia on foot before the border closures but was returned to Greece, where he now lives in refugee housing.

"All my friends have managed to move on" to other European countries, he said. "I'm the only one left. I feel I'm suffocating here."

He was arrested two months ago at a Greek island airport where he tried to board a flight for Italy with a fake Italian passport and a Greek ID card.

Aassim says he applied for relocation and family reunion in Germany but has not heard from authorities. He will now seek asylum in Greece.

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Nicholas Paphitis in Athens contributed to this story.

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Follow Costas Kantouris on twitter: https://twitter.com/CostasKantouris