U2 front man Bono has testified before a Senate appropriations sub-committee on the refugee crisis and violent extremism.

Before sitting at the witness table on Tuesday, Bono posed for photos with three members of Code Pink - which works to end US wars and militarism and support peace and human rights initiatives - who wore pink tiaras and held cardboard torches and signs reading Refugees Welcome.

Cameras whirred furiously as sub-committee chairman Lindsey Graham quipped: "So this is what it's like to be chopped liver."

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

He says in his written testimony that nations teetering on the brink of instability need a better bridge between immediate humanitarian assistance and long-term development.

Bono has foreign aid should be considered an issue of national security, not charity.