U.S. Attorney General Eric Holder is offering law enforcement assistance to help rescue more than 200 Nigerian schoolgirls kidnapped by the Islamist militant group Boko Haram, a senior Justice Department source told The Huffington Post on Monday.

Holder has also ordered an intelligence assessment of Boko Haram, which the United States designated as a terrorist organization in November 2013. The group, whose name means "Western education is sin," receives training from al Qaeda and its affiliates.

"Let me be clear," Secretary of State John Kerry said Saturday during a trip to the Democratic Republic of Congo. "The kidnapping of hundreds of children by Boko Haram is an unconscionable crime, and we will do everything possible to support the Nigerian government to return these young women to their homes."

On April 14, members of Boko Haram invaded a boarding school in Nigeria, pulled 276 girls from their beds and packed them into trucks. At least 53 girls have escaped, while the rest are allegedly being sold as brides to local militants for $12, according to the girls' relatives.

Abubakar Shekau, a man claiming to be the leader of Boko Haram, took credit for the kidnapping in a video obtained Monday by Agence France-Press and said he is selling the girls as wives to prevent them from receiving a Western education.

"I abducted your girls. I will sell them in the market, by Allah," Shekau said, according to a CNN translation. "There is a market for selling humans. Allah says I should sell. He commands me to sell. I will sell women."

Shekau added, "Girls, you should go and get married."

The Nigerian government claims to be handling the situation, but weeks after the kidnapping, Nigerian officials appear to be no closer to finding the missing girls. The government's perceived ineptitude has inspired international protests and the globally trending Twitter hashtag #BringBackOurGirls.

"Access to education is a basic right & an unconscionable reason to target innocent girls," former U.S. Secretary of State Hillary Clinton wrote Sunday on Twitter. "We must stand up to terrorism. #BringBackOurGirls."

The State Department's annual report on global terrorism, released last week, found that Boko Haram "receives the bulk of its funding from bank robberies and related criminal activities, including extortion and kidnapping for ransoms." The group has killed thousands of people in Nigeria since 2009, according to the report.

It is unclear whether Nigeria will accept Holder's offer of help. CNN reported that Nigeria has not yet asked for help from the United States in finding the girls, possibly because they do not want "visible American forces in their country."

CORRECTION: A previous version of this article stated that Holder had offered to send FBI agents to Nigeria. According to HuffPost's source, the attorney general did not specify that FBI agents would be available.