WASHINGTON (AP) – President Barack Obama says his upcoming visit to Cuba will advance U.S. efforts to restore ties with the communist nation and improve the lives of Cubans.

Obama will be making the first trip to Cuba by a sitting president in more than half a century. He says on Twitter there’s already been significant progress.

White House deputy national security adviser Ben Rhodes says the U.S. still has “serious differences” with Cuban President Raul Castro’s government. He says Obama will raise issues of human rights and political freedoms in discussions with Castro.

Rhodes says the U.S. doesn’t want to “impose change” but believes Cuba will benefit from free expression of universal rights.

Obama’s brief stop is planned for March 21-22. The White House says Obama will also visit Argentina.