US-Chinese relations, already tense over the coronavirus pandemic and Beijing's crackdown in Hong Kong, deteriorated once again Wednesday as Washington ordered the closure of the Chinese consulate in Houston within 72 hours. China slammed the US move, which came one day after the unveiling of a US indictment targeting two Chinese nationals for allegedly hacking hundreds of companies worldwide and seeking to steal virus vaccine research. President Donald Trump threatened more consulate closures, telling reporters "it's always possible." "We're setting our clear expectations for how the Chinese Communist Party is going to behave," US Secretary of State Mike Pompeo said during a visit to Denmark. "President Trump has said 'enough,'" Pompeo added. The secretary of state cited the indictment of the two Chinese nationals for computer hacking but did not specifically mention the order to close the Houston consulate. The closure of the Chinese diplomatic installation in one of America's biggest cities marks a dramatic escalation in tensions between the world's top two economies. Washington and Beijing are feuding over a slew of issues ranging from trade to the pandemic to China's policies in Hong Kong, Xinjiang and the South China Sea. Republican Senator Marco Rubio, acting chairman of the Senate Intelligence Committee, called the Houston consulate the "central node of the Communist Party's vast network of spies & influence operations in the United States." Michael McCaul, Republican Leader on the House Foreign Affairs Committee, echoed this, saying the consulate was the "epicenter" of efforts to steal "sensitive information to build up their military." State Department spokeswoman Morgan Ortagus said the consulate was ordered shut "in order to protect American intellectual property and Americans' private information." The State Department said China has engaged in massive spying and influence operations throughout the United States for years. "These activities have increased markedly in scale and scope over the past few years," it said. - 'Outrageous and unjustified' - In Beijing, Chinese foreign ministry spokesman Wang Wenbin said the order to close the consulate was an "outrageous and unjustified move which will sabotage China-US relations." "China urges the US to immediately withdraw its wrong decision, or China will definitely take a proper and necessary response," Wang said. The ministry spokesman claimed the United States "opened without permission Chinese diplomatic pouches multiple times, and confiscated Chinese items for official use." He also said its embassy in Washington had received "bomb and death threats on Chinese diplomatic missions and personnel in the US." Before the closure order was announced, firefighters and police were called late Tuesday to the consulate building over reports that documents were being burned in trash cans in the courtyard, according to local media. The Houston police force said smoke was observed, but officers "were not granted access to enter the building." "Everybody said 'there's a fire, there's a fire,' and I guess they were burning documents or burning papers? And I wonder what that's all about," Trump asked later. The Chinese consulate in Houston was opened in 1979 -- the first in the year the United States and the People's Republic of China established diplomatic relations, according to its website. The office covers eight southern US states -- including Texas and Florida. There are five Chinese consulates in the United States, as well as the embassy in Washington. Chinese state-run tabloid the Global Times launched a poll on Twitter asking people to vote for which US consulate in China should be closed in response, including the ones in Hong Kong, Guangzhou and Chengdu. The United States has an embassy in Beijing plus five consulates in mainland China and one in Hong Kong. - 'Significant challenge' - Trump's administration has ramped up pressure on China on a wide range of issues, imposing sanctions over policies in Tibet and Xinjiang, where an estimated one million Uighurs and other ethnic minorities are believed to have been rounded up and held in re-education camps. The United States has also downgraded relations with Hong Kong after China implemented a new security law which Washington says is in violation of Beijing's promises of autonomy for the territory. Last week, Washington formally declared Beijing's pursuit of territory and resources in the South China Sea as illegal, explicitly backing the rival territorial claims of Southeast Asian countries. Washington has also infuriated Beijing by banning equipment made by telecom giant Huawei and seeking the extradition from Canada of top executive Meng Wanzhou. "We find the China-US relationship today weighed down by a growing number of disputes," deputy secretary of state Stephen Biegun told lawmakers on Capitol Hill Wednesday. "We are up against a significant challenge in China."