Barack Obama has called the head of aid agency Medecins Sans Frontieres to apologise for a US air strike in Afghanistan which killed 22 people.

Responding to the apology this evening MSF say they are still seeking to invoke a never-used body to investigate the bombing of their hospital in Kunduz on Saturday.

The United States has claimed the bombing was a mistake and the strike was intended to hit Taliban forces.

MSF wants the incident investigated by the International Humanitarian Fact-Finding Commission was set up in 1991 under the Geneva Conventions.

The White House said they will investigate the incident and hold those responsible accountable.

"If it is necessary to hold individuals accountable, that will be done," said White House spokesman Josh Earnest.

"In the United States when we make mistakes, we're honest about it. We own up to it," he added.

MSF said they want in independent investigation into the bombing.

"We received President Obama's apology today for the attack against our trauma hospital in Afghanistan. 

“However, we reiterate our ask that the US government consent to an independent investigation led by the International Humanitarian Fact-Finding Commission to establish what happened in Kunduz, how it happened, and why it happened." - Dr. Joanne Liu, MSF International President, said.