AFP, NEW YORK: US regulators Thursday blocked the purchase of the Chicago Stock Exchange (CHX) by a group of investors including the Chinese company Chongqing Casin.

Two years after the announcement of the deal, US Securities and Exchange Commission regulators cited a lack of clarity in the details of the deal, including an inability to identify who exactly would control the exchange.

US congressmen last summer expressed concern at the prospect of a Chinese company being among the largest shareholders of a US stock market—while President Donald Trump also raised the issue during his campaign.

The decision comes as commercial relations between Washington and Beijing remain tense.

US President Donald Trump, denouncing unfair trade, once again threatened trade sanctions against China Tuesday. The next day, Beijing warned against “any sign of unilateralism or protectionism” from Washington.

According to CHX’s proposal, Chongqing Casin would have acquired 29 percent of the Chicago Stock Exchange. The son of Chongqing Casin’s board chairman, a US citizen, would have bought 11 percent of the company. The rest would have been divided among various American groups and individuals.

The SEC assessed that there was not enough information to prove those parties were not somehow linked to the Chinese company.

It also argued it could not be certain that it would be able to access the Chinese shareholder’s accounts if necessary.

Faced with suspicion from the authorities, three other Chinese groups initially looking to invest pulled out last autumn.

Founded in 1882, the Chicago Stock Exchange is one of the oldest in the United States, handling less than 1 per cent of daily trading according to Bloomberg.