RIYADH/WASHINGTON (Reuters) - The Pentagon sent four Yemeni detainees from the Guantanamo Bay military prison to Saudi Arabia on Thursday, launching President Barack Obama’s final flurry of prisoner transfers despite Donald Trump’s demand for a freeze.

A freed Yemeni detainee is hugged by a family member after his arrival at King Khalid International Airport in Riyadh, Saudi Arabia, January 5, 2017. REUTERS/Faisal Al Nasser

It was the first phase of Obama’s plan to move as many as 19 prisoners to four countries - Oman, Saudi Arabia, the United Arab Emirates and possibly Italy - to shrink Guantanamo’s inmate population as much as possible before the Republican president-elect is sworn in on Jan. 20.

There were emotional reunions with families at the royal airport in the capital Riyadh, with one man bending down to kiss his sobbing mother’s feet as she cried “God is great.”

Fifty-five prisoners now remain at Guantanamo. About 40 will still be left by the time Obama leaves office, meaning that he will be unable to fulfill his longstanding pledge to close the controversial facility at the U.S. naval base in Cuba.

Trump has vowed to keep it open and “load it up with some bad dudes.”

The four Yemenis, all captured as part of the Afghanistan conflict and held without trial for up to 15 years, were on a U.S. list recommended for transfer. They were sent to Saudi Arabia because the Obama administration has ruled out returning Yemenis to their homeland, which is engulfed in civil war and has an active al Qaeda branch.

The men were identified as Mohammed Rajab Sadiq Abu Ghanem, Salem Ahmed Hadi bin Kanad, Abdullah Yehya Yousef al-Shibli and Mohammed Bawazir.

Bawazir was among prisoners who protested with a lengthy hunger strike. He was cleared for transfer by an inter-agency review in 2010 and was about to be sent to the Balkans last January but refused because he wanted to go to a country where he had family, a U.S. official said.

Ghanem and Kanad were deemed too risky to release in 2010 but their cases were re-examined and both were declared eligible for transfer last year. Shibli was approved for transfer in 2010.

Slideshow ( 9 images )

FINAL TRANSFERS

The Obama administration notified Congress last month of its intention to make up to 19 additional transfers, Reuters has reported.

Detainees transferred on Thursday or due to leave in coming days make up the bulk of 23 prisoners declared to be safe for repatriation or resettlement.

Despite that, Trump said on Tuesday all of those held at Guantanamo should remain. “These are extremely dangerous people and should not be allowed back onto the battlefield,” he tweeted.

The White House has dismissed his objections and said transfers from Guantanamo, opened by former President George W. Bush to hold terrorism suspects rounded up overseas after the Sept. 11, 2001 attacks, will continue until he takes office.

Of the prisoners left at Guantanamo, 10 face charges in military commissions, including alleged plotters of the Sept. 11 attacks. About two dozen have not been charged but have been deemed too dangerous to release.

It was unclear whether the four detainees who arrived in Saudi Arabia would be released immediately. Last April, the Islamic kingdom - a top U.S. ally - accepted nine Yemenis and put them through a government-run rehabilitation program that seeks to reintegrate militants into society.

“The United States coordinated with the government of the Kingdom of Saudi Arabia to ensure these transfers took place consistent with appropriate security and humane treatment measures,” the Pentagon said in a statement.

Obama, who has called Guantanamo a “recruiting tool” for terrorists, has slowly whittled the number of detainees down from 242 when he took office. Under Bush, the prison came to symbolize harsh detention practices that opened the United States to accusations of torture.

Obama’s efforts to close the prison have been blocked by mostly Republican opposition in Congress, which has barred him from moving any prisoners to the U.S. mainland.