Story highlights 18 who remain are also eligible for transfer

Trump took to Twitter Tuesday to slam additional prisoner transfers

Washington (CNN) The Pentagon announced Thursday that four inmates were transferred from the Guantanamo Bay prison to Saudi Arabia, dropping the prison's population to 55.

Of those remaining, 19 have undergone a security review process and are eligible for transfer.

"The United States is grateful to the government of the Kingdom of Saudi Arabia for its humanitarian gesture and willingness to support ongoing US efforts to close the Guantanamo Bay detention facility," the Pentagon said in a statement.

The news comes amid reports President Barack Obama is attempting to empty the facility as much as possible prior to Inauguration Day.

President-elect Donald Trump took to Twitter Tuesday to slam the administration's transfers from the prison, nicknamed Gitmo.

Read More