The detention happened after British authorities announced they believed all 39 people found dead in a refrigerated container truck in the county last month were Vietnamese nationals.

British authorities will investigate the crimes of people directly involved in the deaths of 39 victims, while Vietnam will handle labor brokers in Vietnam, Nguyen Huu Cau, director of the Nghe An Police Department, told the press in Hanoi on Monday.

"Following the incident in the U.K., some brokers have returned brokerage fees to families whose children have gone missing," Cau said.

The identities of the suspects have not been revealed as the investigation continues.

Cau said some of these suspects have relatives working in the U.K., so they connected them with job seekers at home.

They charged each person up to $49,000, he said.

So far, Nghe An Province in central Vietnam has reported 21 people missing in the U.K. Most of them left the country between April and August this year, from Noi Bai International Airport in Hanoi, Cau said.

Nghe An authorities have joined efforts to collect DNA samples and fingerprints to facilitate the identification of the victims in the U.K. truck disaster.

Police in neighboring Ha Tinh Province have also arrested two persons in connection with the tragedy. They said their questioning of several individuals indicates that they were also involved in other trafficking incidents that have occurred over the past few years. So far, 10 families in Ha Tinh have reported loved ones missing in the U.K.

On October 23, U.K. emergency services discovered the bodies of 38 adults and one teenager, suspected immigrants, in a refrigerated container truck at the Waterglade Industrial Park in Grays, Essex County, east of London.

After first voicing a suspicion that the 39 people were Chinese nationals, British police said Saturday the victims are most likely Vietnamese.

Almost 63,000 people from Nghe An migrated legally to work abroad between 2012 and 2016, according to the International Orrganization for Migration, the highest among Vietnam’s provinces. Ha Tinh was in third place, accounting for about 34,000.

Vietnam reported 490 human trafficking victims last year, according to the U.S.'s 2019 Trafficking in Persons Report.

Some 70 percent of Vietnamese trafficking cases in the U.K. between 2009 and 2016 were linked to labor exploitation, with young people forced to work in cannabis production and nail salons, according to a British government report released in 2018.

Ha Tinh and Nghe An provinces in central Vietnam have long been a source of illegal migration to Britain for people seeking better lives. Migrants often work in nail bars or cannabis farms, heavily indebted and vulnerable to exploitation.