PARIS (Yomiuri Shimbun/Asia News Network) - The Islamic State in Iraq and Syria (ISIS) group tortures its hostages and keeps them in appalling conditions, according to a French journalist who was held by the extremist group for about 10 months.

"I know very well what is going through the minds of the Japanese hostages," Nicolas Henin said in an interview with The Yomiuri Shimbun in Paris. "I'm really worried about them."

Henin was speaking on Wednesday, a day after a video emerged in which two Japanese hostages were threatened with death unless a US$200 million (S$250 million) ransom was paid by Friday.

The deadline expired on Friday afternoon with no further signal from ISIS.

Chief Cabinet Secretary Yoshihide Suga told a press conference the government had not received any new messages from the Islamic State.

"The situation is still difficult, but we'll do our utmost to ensure the release of the hostages as soon as possible," Suga said.

In June 2013, Henin was abducted while collecting material for a story about the conditions in the northern Syrian city of Raqqa, which has effectively become the "capital" of ISIS. Henin, 39, was alone when he was taken captive.

Blindfolded and with his hands bound, Henin was taken by car to a house. His captors took all of his belongings - even his wedding ring - except for his clothes. For the first two weeks, Henin was locked alone in a bathroom in which there was barely enough room to lie down. He was then moved to a room about the size of 10 tatami mats. He was kept there with other American and European hostages, including James Foley, an American journalist murdered by the Islamic State in August 2014.

At one point, there were nearly 20 hostages being held.

FREQUENTLY MOVED AROUND

The hostages were squeezed into cramped spaces. Living conditions were utterly wretched, said Henin.

"The room contained a bucket and a plastic bottle as very primitive toilets. A terrible smell filled the room," Henin recalled. He could hardly ever use bedding, and the hostages slept together in a huddle on a tile floor. They were given two meals a day: Breakfast was yogurt with a few olives, while dinner was a small serving of rice.

After that, Henin was moved to "at least 10" locations. One transfer took two days by car, another took just 10 minutes. He also spent about a month in an underground room with no windows and no clock.

"All the places where I was held were probably in Raqqa and Aleppo [in northern Syria], Henin said.

"Five or six" guards armed with Kalashnikov automatic weapons kept watch over the locations where the hostages were confined. "There was nothing to do in the rooms where we were detained. Some hostages slept for 15 hours a day," Henin said.

A torture room would unfailingly be nearby. At night, the hostages would be given electric shocks or beaten. The groans of pain from their fellow captives would reach the room where the others were kept.

Some of them played card games and chess using the paper boxes used to carry food. "All we did was wait for time to pass," Henin said.

MYSTERIOUS RELEASE

Henin was released in April 2014. He was taken to a house along with three other French journalists.

A week later, he was handed to the Turkish military at the Syria-Turkey border and taken into protection.

There has been speculation that a ransom of US$18 million (S$22.5 million) was paid to secure their release.

"French President Francois Hollande told me directly, 'France didn't pay [ANY MONEY]," Henin said. "Perhaps someone else paid it. I think there was some sort of deal."

About 10 months have passed since Henin was liberated. His hands still shake slightly. "Even now, I still recall what happened several times an hour," he revealed, as tears welled in his eyes.

23 STILL HELD HOSTAGE

At least 23 people, not including the two Japanese hostages currently threatened with death, have been taken hostage by ISIS, according to The New York Times and other sources.

Of this number, 15 people from France, Germany, Spain and other countries have been freed.

Danish photojournalist Daniel Rye Ottosen, 25, was released in June after being held for 13 months. He was taken hostage after entering Syria in May 2013 to take photographs of displaced people and others in the country. The Islamic State demanded 15 million krone (S$2.59 million) in ransom, which the Danish government refused to pay.

However, Ottosen's family and friends called for donations in a Facebook campaign. They are believed to eventually have raised the funds to pay the ransom, partly through loans.

Italian aid worker Federico Motka, 31, was released in May after the Italian government paid about US$6 million in ransom, according to reports by The New York Times and other sources.

At least six hostages have been killed and videos of their beheadings posted online. One of those killed was US journalist James Foley, whom French journalist Nicolas Henin met during his detainment.

Foley was killed in August, shortly after US forces launched airstrikes on ISIS targets. He is believed to have been abused for months, threatened with death and not given food. He also was reportedly forced to convert to Islam and given an Islamic name.