The Doctors Without Borders trauma center is seen in flames, after explosions near their hospital in the northern Afghan city of Kunduz.

The U.S. and Afghan governments vowed on Sunday to jointly investigate the attack on a hospital in Kunduz that killed 22 people, as street-by street battles continued between government forces and Taliban fighters and officials warned of a looming humanitarian crisis for civilians trapped in the city.

Amid accusations that U.S. jet fighters were responsible for what Doctors Without Borders said was a “sustained bombing” of their trauma center in Kunduz, President Barack Obama and Afghanistan’s President Ashraf Ghani promised investigations.

Obama said he expected a full accounting of the circumstances surrounding the bombing, and that he would wait for those results before making a judgment. He said the U.S. would continue working with Afghanistan’s government and its overseas partners to promote security in Afghanistan.

Some top U.S. officials said the circumstances surrounding the incident remain murky, but others indicated the U.S. may have been responsible. Army Col. Brian Tribus, a spokesman for American forces in Afghanistan, said Saturday that a U.S. airstrike “in the Kunduz vicinity” around 2:15 a.m. Saturday morning “may have resulted in collateral damage to a nearby medical facility.”

U.S. Secretary of Defense Ash Carter, speaking to reporters traveling with him on a trip to Spain, said, “The situation there is confused and complicated, so it may take some time to get the facts, but we will get the facts.”

Doctors Without Borders issued a statement Sunday expressing its “clear assumption that a war crime has been committed,” after earlier saying that “all indications” were that the international coalition was responsible for the early Saturday morning bombing. While NATO maintains a significant military role in Afghanistan, airstrikes are conducted by U.S. forces.