Complaints from locals and businesses had led the authorities to investigate mobile signals in the area being disrupted, police said Friday, as cited by Vietnam News Agency.

They found that the Chinese, who were residing in a house in Mong Cai Town near the border, had installed and used a set of mobile signal repeaters, disrupting signals in the area.

Police have seized three antennas, two repeaters, 13 wireless phones, chargers and wires.

The five nationals said they had come to Vietnam to work in trade, and that they were working for the Thanh Dat Trading Company, which is headquartered in HCMC.

Authorities are trying to determine the scale of the Chinese nationals’ violations. The investigation is ongoing.