Answering questions after his speech at the Washington think tank, Mr. Brennan said, “I don’t have a crystal ball that I can say with certainty” that the prison at Guantanamo Bay will be closed on time.

A White House spokesman said the administration remains committed to shutting the prison on schedule and noted Mr. Brennan’s additional comments in response to another question, in which he said, “It is our full intention to close down Guantanamo Bay, per the president’s direction, and we are doing everything possible to ensure that we are able to meet that directive and meet that deadline.”