Obama and Raul Castro

U.S. President Barack Obama pushed Cuba to improve its record on democracy and human rights as he met with President Raul Castro on a historic visit to the Communist island on Monday, but Castro responded by decrying U.S. “double standards”.

Obama said the two had “frank and candid” discussions about human rights as well as areas of cooperation. Castro said they could achieve much better relations if the United States lifted its 54-year-old trade embargo on the island.

“We continue to have serious differences, including on democracy and human rights,” Obama said at a joint news conference, where Castro made the rare step of taking questions from journalists.

In response to a question on political prisoners, Castro angrily demanded to be shown a list of such detainees, reflecting Cuba’s position that it holds no such prisoners.

“Give me a list of those political prisoners right now and if the list exists they will be released before the night is through,” Castro said.

The two leaders held face-to-face meetings a day after Obama arrived for the first visit by a U.S. president in almost 90 years. The trip would for decades have been unthinkable but became possible after secret talks led to a 2014 agreement to normalize relations between the two Cold War-era foes.

The opening ended decades of U.S. efforts to force Cuba to change through isolation. But Obama is under pressure from critics at home to push Castro’s Communist government to allow political dissent and further open its Soviet-style economy.