The leader of the Nigerian Islamist rebel group Boko Haram has offered to release more than 200 schoolgirls abducted by his fighters last month in exchange for its members being held in detention, according to a video posted on YouTube on Monday.
The search for the girls intensified as a senior U.S. administration official said the United States deployed manned surveillance aircraft over Nigeria and was sharing satellite imagery with the Nigerian government.
About 100 girls wearing full veils and praying are shown in an undisclosed location in a part of the 17-minute video in which Boko Haram leader Abubakar Shekau speaks.
Boko Haram militants, who are fighting for an Islamist state, stormed a secondary school in the northeastern village of Chibok on April 14 and seized 276 girls who were taking exams. Some have managed to escape, but about 200 remain missing.
A government official said "all options" were being considered to secure the girls' release.
Nigeria has deployed two army divisions to hunt for the girls, while several countries, including the United States, Britain, Israel and France, have offered help or sent experts.
Nigerian authorities met with some of the experts on Monday and plan further meetings with the West African country's defense and security agencies, a government statement said.
"We have shared commercial satellite imagery with the Nigerians and are flying manned ISR (intelligence, surveillance and reconnaissance) assets over Nigeria with the government's permission," the senior U.S. official said.
In a 1.25-minute segment of the YouTube video, scores of girls in black and grey veils sit on the ground, chant and sing. Shekau, wearing military fatigues and holding an AK-47, then addresses the camera. He appears confident and at one point even laughs.
"All I am saying is that if you want us to release the girls that we have kidnapped, those who have not accepted Islam will be treated as the Prophet (Mohammad) treated infidels and they will stay with us," he said, according to a translation of his words originally spoken in a Nigerian language.
"We will not release them while you detain our brothers," he said, before naming a series of Nigerian cities. It was not clear if he was in the same location as the girls, although the release of the video appeared to signal a willingness on his part to negotiate.
Mike Omeri, a senior Ministry of Information official, told a news conference the government had seen the video.
"The government of Nigeria is considering all options towards freeing the girls and reuniting them with their parents," he said.
The governor of Borno state, where the girls were abducted, said in a statement the video had been distributed to families and local schools in an effort to identify the girls shown.
Security officials said on Monday five militants suspected in two car bombs that killed at least 90 people on April 14 and May 1 in a suburb of the capital, Abuja, had been arrested. Nigeria has arrested hundreds of suspected Boko Haram militants.
There have also been several jail-break attempts. Suspected militants overpowered guards at a prison near the presidential villa in Abuja in March, triggering a gun battle that killed 21 people.
In another incident in the same month, insurgents attempting to free captured comrades fought a two-hour battle at Giwa barracks in the northeastern city of Maiduguri.
Human rights groups have said previously that Giwa barracks has been used to illegally detain and torture suspects, something the military denies.
Summit in France
The Nigerian government has been criticized for its response to the abductions, but President Goodluck Jonathan said on Sunday that international military and intelligence assistance made him optimistic about finding the girls.
A Nigerian military source told Reuters on Monday that two foreign counterterrorism units were already on the ground.
"They have visited Chibok on Sunday for preliminary investigation with our troops and experts before fully kick-starting the rescue mission," the source said.
Jonathan will attend a summit in Paris on Saturday to discuss security in the region. On Monday, he visited the Republic of Congo for talks on the meeting.
"The objective is to deepen the cooperation and partnership between Nigeria and her neighbors," said Jonathan's spokesman, Reuben Abati.
Leaders from Chad, Benin, Cameroon and Niger are also due to attend along with representatives of the European Union, Britain and the United States.
The abductions have touched a chord worldwide and triggered a social media campaign using the Twitter hashtag #BringBackOurGirls. Boko Haram has killed thousands since 2009 and destabilized parts of northeast Nigeria, the country with Africa's largest population and biggest economy.