 -- President Obama apologized to Doctors Without Borders for the airstrike that killed at least 22 people last weekend, White House Press Secretary Josh Earnest announced today.

"This morning from the Oval Office, President Obama spoke by telephone with Doctors Without Borders International President Dr. Joanne Liu, to apologize and express his condolences for the MSF staff and patients who were killed and injured when a US military airstrike mistakenly struck an MSF field hospital in Kunduz, Afghanistan over the weekend," Earnest said in the White House briefing.

“When we make a mistake, we’re honest about it, we own up to it, we apologize where necessary as the president did in this case," Earnest added. "We implement the kinds of changes that make it less likely that those kinds of mistakes will occur in the future.”

The president also phoned Afghan President Ashraf Ghani to "express his condolences for the innocent loss of life in that incident," Earnest said.

MSF International President Dr. Joanne Liu issued a statement in response to the apology, reiterating her earlier call for an independent investigation.

"We received President Obama's apology today for the attack against our trauma hospital in Afghanistan," Liu said in a statement. "However, we reiterate our ask that the U.S. 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."

Last weekend, a U.S. airstrike on a Doctors Without Borders hospital in Kunduz, Afghanistan killed at least 22 people, including a dozen doctors and seven adult patients and three children, according to Doctors Without Borders, anon-governmental organization known internationally by its French name Medicins Sans Frontieres or its acronym MSF.

"Today, we say enough. Even war has rules," said MSF Executive Director Jason Cone said today during a news conference in New York today.

The White House has refrained from offering support for an independent investigation. There are currently three other investigations underway - including one led by the Department of Defense.

"The President assured Dr. Liu that the Department of Defense investigation currently underway 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 that would make tragedies like this one less likely to occur in the future," Earnest said.

The U.S. is also participating in investigations conducted by NATO and in conjunction with the Afghan government.

ABC News' Meghan Kenneally contributed to this report.

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