When the United States ordered China in July to close its consulate in Houston, Assistant Secretary of State David Stilwell also delivered a message to China's ambassador all Chinese military researchers in the United States must be removed.

The July 21 order, only now being reported, came amid the Trump administration's concerns an operation was underway for the researchers to gather scientific intelligence from U.S. universities, under the assistance of Chinese diplomats, reports The Wall Street Journal.

According to court documents, the sources for the intelligence were Chinese postgraduate researchers who had hidden their active military duty statuses with the People's Liberation Army.

Events leading to the consulate's closing are still classified, but according to U.S. officials, the interaction between the researchers and the diplomats was behind the decision to close the facility.

U.S. officials became suspicious about the diplomats when the White House in May restricted future visas for researchers. The Chinese diplomats started removing the researchers from the United States when the FBI started to question some of them and gave them orders considered unusual.

For example, researchers that were brought to China's D.C. embassy were told to reset all their electronic devices, and in another case, diplomats misled the State Department after visiting Indiana to tell an artificial-intelligence doctoral student he could be contacted because of his military background, which was not disclosed on his visa application. 

China's Foreign Ministry is denying any wrongdoing, including accusations of intellectual property theft.

In retaliation for the order to close the Houston consulate, China shut the U.S. consulate in Chengdu. Now, China has four consulates and its D.C. embassy, and the U.S. has four consulates in China, along with an embassy in the mainland.

Four Chinese researchers are facing federal charges of visa fraud, with two pleading not guilty and the other two not yet entering pleas.

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