China announced Thursday that the U.S. had returned four people to China, including three citizens it said had been held for “political purposes.”

The State Department announced the release of Mark Swidan, Kai Li and John Leung. A U.S. government official told NBC News the three were exchanged for two Chinese detainees.

Mark Swidan, Kai Li, and John Leung have been released from detention, a spokesperson for the National Security Council said.