Calls for the United States to help find and free hundreds of schoolgirls kidnapped in Nigeria are mounting after Boko Haram claimed the abduction and threatened to sell the girls as "slaves".
"I abducted your girls," the Islamist group's leader Abubakar Shekau said in a 57-minute video obtained by AFP Monday, referring to the 276 students kidnapped three weeks ago from their boarding school in Chibok, northern Nigeria.
"I will repeat this: Western education should fold up. I abducted your girls. I will sell them in the market, by Allah," Shekau said, adding that his group was holding the girls as "slaves", in comments that stoked international outrage.
US officials said they were worried many of the students, who are aged 16 to 18, had now been smuggled across Nigeria's borders into other countries which could complicate the so-far fruitless efforts to find them.
"We cannot close our eyes to the clear evidence of barbarity unfolding before us in Nigeria," said Democratic Senator Amy Klobuchar, her voice breaking as she addressed the Senate.
As anger and frustration escalates in Nigeria at the government's failure to find the girls, six US senators have introduced a resolution calling for action.
"We and our African allies should do everything to help the Nigerian government rescue innocent girls and return them to their families," Senator Dick Durbin, one of the resolution's sponsors, said in a tweet.
State Department spokeswoman Marie Harf condemned the abduction as "despicable" and said Washington was standing by to assist "in any way we think that is appropriate".
However, she declined to outline specific US help and dismissed suggestions that the US would deploy military assets on the ground.
Undersecretary of State Sarah Sewall is on her way to Nigeria and will meet with senior officials in the coming days to discuss the crisis, Harf said.
Nigeria's President Goodluck Jonathan has been under mounting pressure to act since gunmen stormed the girls' school on April 14, forcing them from their dormitories on to trucks and driving them into the bush.
Fifty-three of the girls managed to escape from the militants but 223 were still being held, police said last Friday.
In his first public comments on the abduction on Sunday, Jonathan pledged that the government would find the girls and bring them home.
"This is a trying time for this country. It is painful," he said, adding that he had sought international assistance in tackling the country's security challenges.
Hours before the girls were taken, the capital Abuja was hit by its deadliest ever attacks, a car bomb on the outskirts of the city that killed 75 people, also claimed by Boko Haram.
A copy-cat bombing in the same spot on May 1 has put the country further on edge as Abuja prepares to host a World Economic Forum summit that opens on Wednesday and includes a visit from Chinese Premier Li Keqiang.
In the latest video, Shekau is seen dressed in combat fatigues standing in front of an armoured personnel carrier and two pick-up trucks mounted with sub-machine guns.
Six armed men stand beside him with their faces covered.
"I abducted a girl at a Western education school and you are disturbed. I said Western education should end. Western education should end. Girls, you should go and get married," he said.
"I will marry off a woman at the age of 12. I will marry off a girl at the age of nine," said the shadowy militant leader, speaking in the local Hausa language and Arabic, as well as English.
Unconfirmed reports from local officials in Chibok indicated the girls had been taken across Nigeria's borders to Chad and Cameroon, and sold as brides for as little as $12.
International attention on the plight of the missing students was initially slow but has grown quickly in recent days, in part because of a social media campaign -- #bringbackourgirls.
One of the campaign's leaders, Naomi Mutah, was arrested on Monday during a meeting with First Lady Patience Jonathan for falsely claiming she was a mother of one of the abducted girls.
Another of the group's leaders, Hadiza Bala Usman, said Mutah was representing mothers who could not make it to Abuja for the meeting with Jonathan and that the first lady had ordered her arrest.
Jonathan's office denied that the first lady was involved. The reported arrest was widely criticised on social media and Mutah has since been released, Usman told AFP.
Unprecedented security has been put in place for the World Economic Forum meeting, but the kidnapping and twin attacks in Abuja have added to long-standing doubts over Nigeria's ability to contain the insurgency.
Boko Haram has been waging an increasingly deadly insurgency in Nigeria's north that has claimed more than 1,500 lives this year alone.
Scores of Boko Haram gunmen riding in armoured vehicles razed a remote northeast Nigeria town of Gamboru Ngala on Monday and opened fire on residents who tried to flee into neighbouring Cameroon, witnesses said.
"They have burnt the market, customs office, police station and almost every shop in the town and killed many people but I can't say how many," Musa Abba said.