TEHRAN, Iran (AP) -- The U.S. and Iran have conducted a prisoner exchange. The trade Saturday involves Chinese-American graduate student Xiyue Wang and Iranian scientist Massoud Soleimani. Iran's foreign minister first announced the swap on Twitter. President Trump shortly after acknowledged Wang was free in a statement from the White House, saying he "is returning to the United States." Iran has detained dual Iranian nationals and those with Western ties in the past to be used as bargaining chips, amid heightened tensions over its collapsing nuclear deal with world powers and sanctions.