Beijing, July 26 (RHC)-- Authorities have tightened security outside the United States consulate in the southwest Chinese city of Chengdu as American staff prepared to leave, a day after China ordered it to close in response to a U.S. order for China to shut its consulate in Houston.

The tit-for-tat closures represent a sharp deterioration in relations between the countries, which have the world's two largest economies, with China's foreign affairs ministry on Saturday accusing the U.S. of violating international and bilateral agreements.

The accusation comes soon after a group of men who appeared to be U.S. officials were seen forcing open a back door to the Houston facility after the closure order took effect on Friday.   China's foreign affairs ministry promised to respond to the incident, but did not elaborate on how.

"As for the US side's forcible entry into the premises of the Chinese Consulate General in Houston, China expresses strong dissatisfaction and resolute opposition," the ministry said in a statement.  "China will make a proper and necessary response to this." 

In Chengdu on Saturday, spectators snapped photos outside the US consulate as police in T-shirts and surgical masks stood on the sidewalk and the closed-off street in front of the walled compound.

The U.S. consulate emblem inside the compound was taken down and staff could be seen moving about. Three moving vans were later seen in the compound.