In a move to locate the missing Nigerian schoolgirls abducted by rebel group Boko Haram, the US has sent manned and unmanned surveillance aircraft to the West African nation.

Reuters has reported that US officials stated a drone known as a ‘Global Hawk’, which is a high-altitude unmanned spy plane, has been deployed to aid the search for the missing girls.

Last month militant rebel group Boko Haram kidnapped more than 200 Nigerian schoolgirls from their secondary school in Chibok, a town in northeastern Nigeria.

According to reports only 43 girls managed to escape, and the rest are still missing.

However, following public outcry and delayed reaction by the Nigerian government to rescue the girls, a global social media campaign with the hashtag #BringBackOurGirls took off.

Activists and celebrities have taken to social media networks such as Twitter, Facebook, and Instagram to vent the world’s anger at the situation using the hashtag.

Intensified global focus on the tragedy, in turn, has prompted the US, Britain, France and Israel to help locate the missing girls.

And thus far, the US has sent military, law-enforcement and development specialists, according to Reuters.

Speaking at the World Economic Freedom (WEF) in Abuja last week, Nigerian President Goodluck Jonathan also vowed to rescue the girls.

"I believe that the kidnap of these girls will be the beginning of the end of terrorism in Nigeria," he said.

Despite various efforts to find and return the girls home, their whereabouts have still not been determined.

Instead, a new video released earlier this week featuring group leader Abubakar Shekau showed more than 110 girls sitting on the ground in a rural location dressed in full Islamic veils.

This is the first time they have been seen in captivity, Reuters reported.

It has also been reported that 77 of the girls in the video have been identified by parents, fellow students and girls who escaped the abductions.

In the video the leader of Boko Haram has only offered to release the girls in exchange for prisoners held by the government.

Meanwhile, there have been further reports that Al-Qaeda-linked Somali rebel group Al-Shabaab has dismissed reports that the Nigerian schoolgirls were kidnapped by Boko Haram.

It claims the girls left their school voluntarily to join the terror group and convert to Islam, according to eNCA.com.