Vietnam’s foreign minister demanded stricter penalties for human traffickers after 39 migrants, most of them from the South Asian country, were discovered dead in a truck in England last month.

“Vietnam strongly condemns human trafficking and considers it a serious crime; traffickers must be strictly dealt with,” said Li Thi Thu Hang, a spokeswoman for the foreign ministry, in a statement posted to the country’s website Saturday.

Hang said Vietnam was working closely with British police to verify the identity of the 31 men and eight women who died in the refrigerated truck, which was found last month in Grays, about 25 miles east of London.

Authorities arrested two men in Vietnam and one man in Ireland in connection with the deaths. Police are searching for two other suspects who they say are part of a global ring of international human smugglers.

“This is a humanitarian tragedy,” Hang said, calling on other countries to join together in the fight against human smugglers.