Authorities have detained 341 foreign nationals working illegally in the first crackdown targeting asylum seekers in areas under the jurisdiction of the Tokyo and Nagoya immigration bureaus, an effort aimed at curbing alleged abuse of Japan’s refugee system.

The Justice Ministry announced Tuesday that of the foreign nationals detained in the crackdown conducted between Nov. 6 and Dec. 1, 94 men and women were awaiting the government’s decision on whether to grant them refugee status. Others included visa overstayers and people engaged in activities other than those permitted under their visa status.

“The number of applications for asylum with an aim to secure jobs, which we can’t approve of, is on the rise, so we need to adopt stricter measures while processing those applications,” ministry official Hiroshi Kimizuka told reporters. “But we also need to strengthen efforts in detecting people who successfully went through the screening process and have been working illegally (in Japan).”

Before a revision to the refugee system that took effect in January, applicants for refugee status could be granted a temporary work permit six months after applying for asylum in Japan. The ministry stopped issuing such permits in January.

Kimizuka, who serves as director of the Enforcement Division at the ministry’s Immigration Bureau, said that 81 asylum seekers detained in November had been working during the six-month period when they were supposed to await their work permit. The remaining 13 failed to renew their visa status after applying for refugee status — the procedure required to be allowed to work in Japan. By the end of January, 80 of the detained asylum seekers withdrew their applications for refugee status after their misconduct came to light, the ministry said. Nearly all of them admitted they had come to Japan to work and have been sent back to their home countries, according to Kimizuka. Of the 341 captured in the crackdown, 257 left Japan by the end of January.

Among the 341 detainees, 218 worked illegally in and around Tokyo. The authorities confirmed the highest number of illegal workers in Ibaraki Prefecture, with 102 such cases. Another 95 were caught in Aichi Prefecture. The largest numbers of the detainees worked in food processing, agriculture and construction. Kimizuka said that immigration bureaus in Tokyo and Nagoya in particular have been flooded with applications for refugee status in recent years. He added that over 73 percent of asylum seekers in 2016 filed applications with Tokyo’s Immigration Bureau; Nagoya handled around 24 percent of the total applications that year.

“This may have something to do with many opportunities for employment in those areas,” Kimizuka said.

Vietnamese represented the largest group of foreign nationals detained in November, at 108, followed by 68 Thais, 53 Chinese and 46 Filipinos. According to the ministry, the number of foreign nationals who applied for refugee status last year reached a record high of 19,628. Over the course of the year, 20 people were given refugee status and 9,730 such applications were rejected, according to ministry figures. The acceptance of only 20 asylum seekers last year is likely to fuel growing criticism Japan has faced for its reluctance to accept migrants despite its aging population.

Kimizuka said that among asylum seekers are people who entered Japan with student visas or through the Technical Intern Training Program — a system created in response to labor shortages for low-level jobs — and applied for refugee status after their visas expired.

“The surge in asylum seekers working illegally is a continuously growing problem,” Kimizuka said. “Many people overstay their visas and try to earn as much as they can until they get caught by authorities.”

This has become “typical conduct” of visa entrants disguising the real purpose for entering the country, he added.