President Obama on Wednesday apologized to Doctors Without Borders for the American air attack that killed at least 22 people at a medical clinic in Afghanistan, and said the U.S. would examine military procedures to determine whether changes could prevent such incidents.

Obama's apology came four days after the facility in the northern city of Kunduz came under fire from what was later determined to be a U.S. aircraft. The attack outraged aid groups and complicated U.S. efforts in Afghanistan.

White House spokesman Josh Earnest said Obama called the organization's international president, Joanne Liu, and offered condolences to the group's staff.

"When the United States makes a mistake, we own up to it, we apologize where appropriate, and we are honest about what transpired," Earnest said.

A day earlier, the White House had stopped short of an apology, waiting to learn more even while acknowledging the attack was a U.S. mistake.

Obama told Doctors Without Borders that the U.S. would review the attack to determine whether changes to U.S. operating procedures could reduce the chances of a similar incident, and that those responsible for the Kunduz attack would be held accountable, if appropriate, Earnest said.

Obama also spoke to Afghan President Ashraf Ghani to convey condolences and pledge continued cooperation, the White House said.

Investigations by the U.S., NATO and the Afghan government are underway, but Doctors Without Borders has said more are needed. Doctors Without Borders wants a fact-finding mission to determine whether the attack violated the Geneva Conventions.

Obama restated his commitment to a thorough and transparent investigation by the Defense Department, Earnest said. He didn't specifically address the group's call for an independent probe.