VIDEO-McCain The Lead with Jake Tapper

(CNN) – Terrorist group Boko Haram's kidnapping of 276 Nigerian school girls last month is an "offense against humanity," says Republican Sen. John McCain.

Six U.S. military advisers arrived in Nigeria Friday, a U.S. official told CNN. They will join a team of U.S. and British officials already in the country, helping find the girls, planning rescue efforts, and devising strategies to help subdue Boko Haram.

"I hate to use the words if I were president, so I won't. But what we should have done as soon as we knew these young girls were kidnapped ... we should have utilized every asset that we have, satellite, drones, any capabilities that we had to go after them," McCain said in an interview with CNN's "The Lead with Jake Tapper.""We should have mounted a humanitarian mission," says McCain.

Acknowledging the difficulties of Nigeria's geography and terrain, McCain insists the U.S. should have used every asset available.

For more of our interview with Sen. John McCain, check out the video above.