The Chinese consulate in Houston, Texas, was closed down to disrupt the espionage and influence activities being run out of it, which rose to a level that threatened the United States' national security, senior Trump administration officials said.
In a briefing for reporters on Friday, they laid out the most comprehensive set of allegations of the consulate's illegal activities since it had been ordered to close on Tuesday, adding that other Chinese consulates in the US also engaged in similar behaviour.
The Houston consulate was implicated in an investigation of grant fraud in a Texas research institution, with consulate officials directly involved in communications with researchers and guiding them on what information to collect, said a senior Justice Department official.
The Houston consulate, along with other Chinese consulates in the US, also promoted international talent recruitment programmes, which can create incentives to steal intellectual property and create conflicts of interest, the official said.
He cited the conviction of Houston businessman Shan Shi of trade secret theft in July last year.
The Chinese-American businessman had established a subsidiary of a Chinese firm and poached local talent as well as trade secrets from a local business to develop syntactic foam. The buoyancy material helps keep offshore oil and gas drilling equipment afloat and is technology that China wants to be self-sufficient in, said the official.
"The sum total of the Houston consulate's activities went well over the line of what we were willing to accept, and unless we disrupted it, it threatened to become even more aggressive in Houston and at other Chinese consulates nationwide," said the official, speaking on condition of anonymity.
The Trump administration on Tuesday ordered the closure of the Houston consulate, one of China's six diplomatic missions in the US including its embassy in Washington, placing it at the centre of the latest diplomatic firestorm and escalation of US-China tensions.
Diplomats were given 72 hours to vacate the premises, a deadline that expired on Friday, local time.
China responded by announcing the closing of the American consulate in Chengdu on Friday.
At the briefing, the officials said Houston and other consulates were also bases of operation for China's Operation Fox Hunt agents sent from China to coerce Chinese dissidents and refugees to return to mainland China.
In one instance, a Houston consulate representative delivered a letter to a person in the South, allegedly from his father, imploring him to return to China.
"The folks in Houston were very much active participants in all the various efforts of collection and influence that the Chinese government, the Chinese Communist Party, is doing here in the US," said a Federal Bureau of Investigation official.
Consulates also enable the direct lobbying of state local officials as well as business people to favour Chinese interests, said officials.
"While that's to be expected of diplomats, when it takes a turn towards the coercive or covert, that becomes a national security problem," said an official.
Consulates were also suspected to run networks of watchers on school campuses that report on fellow students, undermining the freedom of expression that students on American campuses were entitled to, he added.
Officials said that they would not necessarily prosecute consulate staff, as they enjoyed diplomatic immunity.
An official said the closure of the Houston consulate - "one of the worst offenders" - was meant to send a message to remaining officials in other Chinese consulates to stop their illegal activities.
"I don't think you can point to one moment that was the straw that broke the camel's back. It was an increase in malign activity over time and, at some point, you say enough is enough," he said.