Jeff Woodke, an American aid worker held hostage in West Africa for more than six years, has been released, according to U.S. national security adviser Jake Sullivan. 

Woodke was taken from his home in Abalak, Niger, in 2016 by a terrorist network that operates across Mali, Niger and Burkina Faso. He was released outside of Niger in the Mali-Burkina Faso area, a senior administration official said. 

"I'm gratified & relieved to see the release of U.S. hostage Jeff Woodke after over 6 years in captivity," Sullivan tweeted Monday morning. "The U.S. thanks Niger for its help in bringing him home to all who miss & love him. I thank so many across our government who've worked tirelessly toward securing his freedom."

National Security Council spokesperson John Kirby said Woodke will be reunited with his family following a full medical check. 

"There were no concessions made. There were no swaps here," Kirby said. "This was just hard, grueling, deliberate work by diplomats and other experts directly with the government of Niger to get him home." 

Woodke lived in Niger for years before he was taken, helping people groups in the Sahel region. 

U.S. Secretary of State Antony Blinken visited Niger as part of a trip to Africa last week. 

During an unrelated event Monday, the president said he was proud to announce Woodke's return, and noted his administration is working to bring all Americans held hostage home. 

Also on Monday, the nonprofit group Reporters without Borders announced that French journalist Olivier Dubois was released after being hostage for 711 days by an armed group affiliated with Al Qaeda in the Sahel. The nonprofit group said the journalist resurfaced, "free and smiling," on Monday in Niger's capital. 

"We are overjoyed and hugely relieved," said Christophe Deloire, secretary-general of Reporters Without Borders. "We had received reassuring news about Olivier Dubois on several occasions in recent months, and again very recently. He seemed to be in good shape but the length of his captivity worried us. We thank the French authorities for doing what was necessary to obtain his release. It is to France's credit that it does not abandon its citizens when taken hostage, and works to get them freed. Our thoughts are with his family, especially his partner and his son. We salute all those who took part in the campaign for his release."