U2's Bono testifies before Congress on the refugee crisis

"This is unthinkable stuff," he said. "And you should be very nervous in America about it."

Africa, in particular, is grappling with what Bono called a phenomenon of three extremes — ideology, poverty and climate.

"Those three extremes make one unholy trinity of an enemy and our foreign policy needs to face in that direction," he said. "It's even bigger than you think."

Bono said he understood the financial stress the U.S. and other nations are under as they debate how much foreign aid to allot. But he warned the bills will only get bigger without action.

"If you don't do it now, it's going to cost a lot more later," he said. "I do know that."

Bono also suggested using comedy to fight extremist groups. "It's like, you speak violence, you speak their language. But you laugh at them when they are goose-stepping down the street and it takes away their power," he said. "So I am suggesting that the Senate send in Amy Schumer and Chris Rock and Sacha Baron Cohen, thank you."

In Syria, five years of violence has killed more than 250,000 people and displaced another 11 million from their homes. Nearly 174,000 migrants have reached Europe by sea since the beginning of this year alone and 723 are missing or dead, many drowning in the cold, rough waters, according to the International Organization for Migration.

Before sitting at the witness table, Bono posed for photos with three members of the anti-war group Code Pink, who wore pink tiaras and held cardboard torches and signs reading "Refugees Welcome."

Cameras whirred furiously as Republican Sen. Lindsey Graham, the subcommittee chairman, quipped, "So this is what it's like to be chopped liver." Bono took part in a congressional delegation led by Graham that had just returned from Africa and the Middle East.

Bono co-founded the One Campaign, an advocacy group that works to end poverty and preventable disease.