TOKYO (Reuters) - A Vietnamese man who complained of pain before dying of a stroke at a Japanese immigration detention center was left lying on the floor for hours before the guards called an ambulance, a government document said, suggesting that deficiencies in monitoring remain in the country’s detention system.

FILE PHOTO: An inside view of a shared cell is seen at the East Japan Immigration Center in Ushiku, Ibaraki prefecture, Japan March 19, 2015. REUTERS/Yuya Shino/File Photo

The death of 47-year-old Nguyen The Huan, also known as Nguyen The Hung, was the 13th in Japan’s immigration detention system since 2006, a toll that has provoked criticism about conditions inside.

For a week before his death, Nguyen had been groaning and complaining of headaches and neck pain, according to a report by the East Japan Immigration Centre reviewed by Reuters, and was moved to a solitary cell for monitoring.

Guards heard him groaning through an intercom on March 24 and checked on him. They saw him lying on the ground, seemingly asleep. After six hours, when guards noticed that his posture hadn’t changed, they entered the room to find him unconscious and not breathing. They began CPR and called an ambulance.

The previously unreported details show Nguyen died under similar circumstances to a 2014 death of a Sri Lankan detainee. A Reuters investigation of that case found that guards did not call an ambulance until hours after the detainee suffered a heart attack because they had thought he was asleep.

“This death is the same (as the Sri Lankan’s). They both died because they were left alone,” said a member of the watchdog who had read the internal report. “The guards haven’t learned.”

The member, who declined to be identified due to the sensitivity of the case, said there should be a system for monitoring the vital signs of ill detainees around the clock and that guards should at least call on sick detainees to see if they are all right.

Daisuke Akinaga, an official at the East Japan Immigration Centre, declined to comment on the details of Nguyen’s death but said the center did not think there were problems with how it responded. He added that the justice ministry was investigating. The ministry said it could not comment on the center’s response as the investigation was ongoing.

In April, a full-time doctor began working at the East Japan center on weekdays, though there is still no doctor on site around the clock. Guards received emergency medical training twice a year, Akinaga added.

Nguyen came to Japan in the 1990s to seek asylum, a Vietnamese nun had told Reuters. He was held for overstaying his visa and for a drug offense, the report said.