The United States ordered the consulate closed this week, leading China to retaliate on Friday by telling Washington to shut its consulate in the city of Chengdu, as relations between the world's two largest economies deteriorate.

In a briefing for journalists on Friday, a senior State Department official linked espionage activity at the Houston consulate to China's pursuit of research into a vaccine for the new coronavirus.

The official said China had been very clear about its intent to be first to the market with a coronavirus vaccine.