The US government has imposed sanctions on a Cambodian senator alleging he is at the heart of a sprawling scam network, as the Southeast Asian nation comes under intense pressure – including from China – to eliminate a cybercrime industry worth nearly US$20 billion a year.

The US Treasury tagged Senator Kok An, a tycoon with close ties to former leader Hun Sen whose son is now prime minister, and 28 other associates as “specially designated nationals” suspected of controlling “scam compounds throughout the country” that have fleeced millions of dollars from Americans.

This sanction freezes all US assets and entities linked to the named parties, and bars any American national from dealing with them – a significant move that heaps legal risk on banks and businessmen with any exposure to the designated individuals.

Under a Scam Centre Strike Force, US officials have intensified their work against Southeast Asia’s cyber criminals in recent months, belatedly recognising the security risks posed to Americans by a region-wide crisis that targets vulnerable people with bogus promises of love or high investment returns.

“Kok An and his affiliates’ network of scam centres, operating out of casinos and office parks retrofitted for fraudulent activity, launders victims’ funds and provides a base to target US citizens and commit human rights abuses with impunity,” the Treasury said in a statement late on Thursday, adding that taking the networks down was a leading priority for the Donald Trump administration.

Kok An’s ties to the Hun Sen family have also raised awkward questions about the proximity between alleged scam kingpins and Cambodia’s dominant political dynasty.