By Karl Plume, Hallie Gu and Keith Zhai

CHICAGO/BEIJING/SINGAPORE (Reuters) - State-owned Chinese firms bought at least three cargoes of U.S. soybeans on Monday, even as sources in China said the government had told them to halt purchases after Washington said it would eliminate special treatment for Hong Kong to punish Beijing.

The purchases, totaling at least 180,000 tonnes of the oilseed, were for shipment in October or November, the peak U.S. soy export season when American soybeans are usually the cheapest in the world, three U.S. traders with knowledge of the deals said.

It was not immediately clear why buying continued after Beijing's message to state-owned firms, but U.S. traders said Chinese importers still have not covered a large share of October and November soybean needs.

"It's murky, really hard to say," said one U.S. export trader. "Maybe they wanted to knock a few cents off the price, or maybe there's some other agenda. The do need the beans."

Earlier, two sources familiar with the matter said China told state-owned firms to halt large-scale U.S. soybean and pork purchases. One of them said state purchases of U.S. corn and cotton have also been put on hold.

The soybean sales on Monday were small compared to recent purchases by state-owned firms totaling 1 million tonnes or more at a time.

China is ready to suspend imports of more American agriculture products if Washington takes further action on Hong Kong, the sources said.

Any sustained halt in buying would further threaten progress in meeting goals set in the Phase 1 trade deal signed in January. China pledged to significantly boost purchases of U.S. agricultural products, after slashing imports during the bruising trade war.

The U.S. Department of Agriculture and U.S. Trade Representative's office did not immediately respond to requests for comment.

Chinese foreign ministry spokesman Zhao Lijan told reporters during a daily briefing Tuesday that he was unaware of the situation.

On Friday, U.S. President Donald Trump said he was directing his administration to begin the process of eliminating special treatment for Hong Kong in response to China's plans to impose new security legislation. China said on Monday it will counter U.S. attempts to harm Beijing's interests.

(GRAPHIC - Value of U.S. agriculture exports to China: https://fingfx.thomsonreuters.com/gfx/ce/yzdvxdxdzvx/USAGExportstoChinaMar2020.png)

Chinese importers canceled 10,000 to 20,000 tonnes of American pork shipments, equivalent to roughly one week's orders in recent months following Trump's comments on Friday, the source said.

In a worst-case scenario, if Trump continues to target China, Beijing will scrap the Phase 1 deal, a second source familiar with the government plan said.

"There's no way Beijing can buy goods from the U.S. when receiving constant attacks from Trump," the person said.

U.S. corn, wheat and lean hog futures weakened on Monday due to concerns about rising trade tensions. Soybeans were flat. [GRA/]

Under the initial trade deal, China pledged to buy an additional $32 billion worth of U.S. agriculture products over two years above a baseline based on 2017 figures.

The USDA reported that China bought $1.028 billion worth of soybeans and $691 million of pork in the first quarter of 2020. China also bought corn, wheat and soyoil this year.

China has also been purchasing soybeans in recent weeks from Brazil, during that country's peak export season.

Private Chinese importers have not received a government order to suspend all buying, although commercial buyers are very cautious, according to a third source with a major trading house.

"A certain scale of trade will be halted" but it is not a full stop, said a fourth source familiar with government plan.

China could easily find other sellers of farm products, he added.

The sources all declined to be named due to the sensitivity of the matter.

(Reporting by Hallie Gu and Jing Xu in Beijing, Keith Zhai in Singapore and Karl Plume in Chicago; additional reporting by Dominique Patton and Gabriel Crossley in Beijing, Gavin Maguire in Singapore, Tom Polansek and Mark Weinraub in Chicago; editing by Matthew Lewis, David Gregorio and Jason Neely)