US President Barack Obama on Wednesday called the head of medical charity Doctors without Borders (MSF) to apologize for the deadly US air strike on a hospital in the Afghan city of Kunduz, the White House said.

Obama called MSF chief Joanne Liu "to apologize and express his condolences," spokesman Josh Earnest told reporters. MSF has demanded an international probe into Saturday's strike, which killed 22 people, and which the US military has called a mistake.