The Chinese military launched drills around Taiwan on Saturday as a “stern warning” over what it called collusion between “separatists and foreign forces,” its defense ministry said, days after the island’s vice president stopped over in the United States.

Taiwanese Vice President William Lai’s recent trip to Paraguay to reinforce relations with his government’s last diplomatic partner in South America included stops in San Francisco and New York City. The mainland’s ruling Communist Party claims democratic Taiwan as part of its territory and says it has no right to conduct foreign relations.