Jeff Woodke, an American aid worker who has been held hostage in Africa since 2016, has been freed Monday, National Security Adviser Jake Sullivan announced. 

Sullivan tweeted that he is "gratified & relieved to see the release of U.S. hostage Jeff Woodke after over 6 years in captivity. 

"The U.S. thanks Niger for its help in bringing him home to all who miss & love him," Sullivan said. "I thank so many across our government who’ve worked tirelessly toward securing his freedom." 

Woodke was kidnapped from his home in Abalak, Niger, in October 2016 by men who ambushed and killed his guards and forced him at gunpoint into their truck, where he was driven north toward Mali’s border. 

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Jeffrey Woodke in Niger's airport

French journalist Olivier Dubois, left, and American aid worker Jeffery Woodke, center, arrive at the VIP lounge at the airport in Niamey, Niger, Monday March 20, 2023. Dubois was freed alongside Woodke on Monday. (AP/Judith Besnard)

A senior Biden administration official who briefed reporters Monday on Woodke's release described the action as the culmination of years of efforts but declined to say what exactly led to him being freed from captivity or where he is now. 

The official also said no ransom was paid, and no concessions were made as part of securing the 61-year-old's freedom. 

Jeffrey Woodke hostage is released

American aid worker Jeffrey Woodke was detained in October 2016, officials say. He was freed on Monday, March 20, 2023. (FBI)

A source close to Woodke told Fox News in 2018 there was some indication that he was straddling the border between Niger and Mali and was being kept alive as something of a "bargaining chip." 

U.S. officials, according to the AP, said Monday that Woodke was not freed in Niger but in the surrounding region that includes Mali, where Dubois was abducted in 2021.

In an interview with the New York Times, Woodke’s wife Els, of McKinleyville, California, said she was told Jeff is in Niamey, the capital of Niger. 

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Jeff Woodke's wife Els speaks

Els Woodke speaks about the 2016 kidnapping of her husband Jeff Woodke in West Africa during a news conference in Washington, D.C., on Nov. 17, 2021. Jeff Woodke was released on Monday, the Biden administration says. (AP/Cliff Owen)

"He is safe," she said, adding "I don’t yet know if he is healthy." 

In a statement released through a family spokesperson, Els Woodke also said she "praises God for answering the prayers of Christians everywhere who have prayed for this outcome," the Associated Press reported. 

The FBI previously has said Woodke has worked in Niger for more than 25 years. 

The identities of Woodke's captors have not been disclosed. 

US Secretary of State Antony Blinken in Niger

U.S. Secretary of State Antony Blinken, left, is seated with Nigerien Foreign Minister Hassoumi Massoudou at the Diori Hamani International Airport, in Niamey, Niger, on Thursday, March 16. The meeting happened days before Woodke's release was announced. (Boureima Hama/Pool Photo via AP)

While no group has publicly claimed responsibility for Woodke's kidnapping, an array of jihadist militants with Al Qaeda ties are known to operate in the region.

U.S. Secretary of State Antony Blinken, who visited Niger last week, hailed Woodke's release Monday as "very good news."

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"I want to thank the government of Niger where I was just last week for its important assistance in bringing him home. I also want to thank our team starting with special envoy Roger Carstens. All of those who have been working at the Department to bring him home -- tireless efforts, and I'm very pleased that we are now seeing that come to fruition today," Blinken told reporters.

"As you know I have no higher priority or focus than bringing home any unjustly detained American, wherever that is in the world," Blinken added. "We won't rest until they are all home and like Jeffrey, reunited with their families."

Hollie McKay and the Associated Press contributed to this report.