The State Department has faced a barrage of congressional criticism after Malaysia, a key US trading partner, was kept off a blacklist of countries that fail to meet minimum standards against modern-day slavery.
Susan Coppedge, ambassador-at-large to monitor and combat trafficking in persons, will meet Deputy Prime Minister Ahmad Zahid Hamidi, during her two-day visit to the main city Kuala Lumpur starting Monday.
The department says there are several million migrant laborers in Malaysia and more than 150,000 registered refugees and asylum-seekers who are also vulnerable to traffickers.
The Obama administration controversially took Malaysia off its human trafficking blacklist in 2015 although it had secured only a handful of human trafficking convictions in the previous year.
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The administration denied accusations of political interference driven by Malaysia's participation in the US-backed Trans-Pacific Partnership trade agreement.
The watch list ranking was renewed in the department's latest human trafficking report issued three weeks ago, which found that the Malaysian government questioned several officials in connection with the mass graves but did not prosecute any officials last year for complicity in trafficking crimes.
Several lawmakers pressed Coppedge on the issue at congressional hearings July 12. She agreed that it was "troubling" that no government officials have been prosecuted or held accountable.