WASHINGTON (Reuters) - U.S. President Barack Obama telephoned the head of Medecins Sans Frontieres and apologized for a deadly air strike on the aid group's hospital in Kunduz, Afghanistan, that killed 22 people over the weekend, the White House said on Wednesday.

On the call with the medical charity's president, Joanne Liu, Obama also said the U.S. investigation into the incident would "provide a transparent, thorough and objective accounting of the facts and circumstances of the incident. And that, if necessary, the president would implement changes to make tragedies like this one less likely to occur in the future," White House spokesman Josh Earnest told reporters.

MSF, also known as Doctors Without Borders, is calling for an independent international fact-finding commission to probe the bombing, which it deems a war crime. Among those killed were 12 MSF staff..

Earnest said "there is no evidence that ... I've seen or that anybody else has presented that indicate that this was anything other than a terrible, tragic accident."

He added that the Pentagon's investigation will look into the conduct of individuals involved in the attack as well as the rules of engagement.

Obama also called Afghan President Ashraf Ghani to express condolences for the lives lost of patients and staff during the strike, Earnest said.

(Reporting by Lisa Lambert, Roberta Rampton and Doina Chiacu; Editing by Susan Heavey and Sandra Maler)