A Saudi man held in the US military prison at Guantanamo Bay, Cuba, will not be released on Tuesday as spelled out in a 2014 plea agreement, the Pentagon said.

The plea agreement signed by Ahmed Mohammed Ahmed Haza al-Darbi calls for him to be transferred from the detention facility to Saudi Arabia four years after signing the plea agreement.

Pentagon spokeswoman Navy Commander Sarah Higgins said in an email to dpa the Department of Defence is waiting for assurances from the Saudi government to move forward with the transfer.

"Al-Darbi will remain at Guantanamo until all transfer details are concluded," Higgins said. "Thus far, al-Darbi has complied with all terms of his plea agreement. [The Department of Defence] hopes the transfer will take place soon."

The Saudi embassy in Washington did not return a call from dpa seeking comment about al-Darbi's pending transfer.

Al-Darbi, 43, pleaded guilty to terrorism and other war crimes in exchange for his release to his homeland, according to the Miami Herald.

After the plea deal was announced on February 20, 2014, he testified against two other men being held at Guantanamo and awaiting trial on terrorism and other charges.

Al-Darbi has been in US military custody since August 2002 and at the prison at Guantanamo Bay since March 2003, according to the Herald. He is one of 41 inmates still held at the prison.