BEIJING (AP) — U.S. Senator Steve Daines is visiting Beijing as the U.S. and China swap tariff threats and harsh words over each others' handling of the illegal trade in fentanyl.

Daines, a strong supporter of President Donald Trump, is in the country for three days of meetings starting Friday, the American Embassy reported.

Daines previously worked as an executive for U.S. companies in China and served as a go-between during Trumps’ first term in office when tariffs were also a major issue. Daines’ schedule hasn’t been made public, but an official has said off the record that he is expected to meet with a deputy Chinese foreign minister. That would make him the most senior U.S. representative to meet with a Chinese official since Trump took office.

Trump is expected to speak with President Xi Jinping either by phone or in a face-to-face meeting.

U.S.-China tensions have spiked as the U.S. imposed 20% duties on Chinese goods, drawing retaliatory tariffs of 15% on U.S. farm goods from China this past week. The U.S. accuses China of doing too little to stop the export of precursor materials for fentanyl, a highly potent opiate blamed for tens of thousands of deaths in the U.S.

China responded with a report detailing its efforts to control the illegal trade in fentanyl, specifically the ingredients for the opioid that are made in China, and the foreign minister blasted the U.S. for responding to Beijing’s goodwill with tariffs.

The report said that China and the U.S. have held multiple high-level meetings since early last year to promote cooperation, and that its Narcotics Control Bureau holds regular exchanges with the U.S. Drug Enforcement Agency.

China is committed to cooperation, the report said, “but firmly opposes the U.S. imposition of unlawful sanctions and unreasonable pressure on China on the pretext of responding to fentanyl-related issues.”