President Obama on Wednesday informed House Speaker John Boehner that 80 U.S. military personnel had been sent to the central African nation of Chad as part of efforts to help locate nearly 300 schoolgirls kidnapped by Islamist militants in Nigeria last month.
Chad borders Nigeria, where members of Boko Haram abducted the girls from the city of Chibok in April.
"These personnel will support the operation of intelligence, surveillance, and reconnaissance aircraft for missions over northern Nigeria and the surrounding area," the president said in the letter to Boehner.
"The force will remain in Chad until its support in resolving the kidnapping situation is no longer required," he said.
Obama said the letter was meant to keep Congress informed "consistent with the War Powers Resolution."
NPR's Tom Bowman says that most of the 80 are U.S. Air Force personnel charged with operating Predator surveillance drones.
The Associated Press says dozens of the girls and young women have escaped from captivity, but 276 are still held.
Boko Haram has threatened on video to sell most of them into slavery if the government does not release detained militants, the AP says.
The government of Nigerian President Goodluck Jonathan came under intense criticism for its initial response to the kidnappings. Since then, the international community has pledged its assistance, the news agency says.