The Pentagon says it is trying to determine how a deadly US airstrike hit a hospital run by Medecins Sans Frontieres (Doctors Without Borders) in the Afghan city of Kunduz.

US Defense Secretary Ash Carter said in a Saturday statement that "a full investigation into the tragic incident is under way in coordination with the Afghan government."

He said the area around the hospital had been the scene of intense fighting in recent days with US forces supporting Afghan Security Forces against Taliban militants.

US forces launched the airstrike at 2.15 a.m. (2145 GMT) on the MSF hospital where they admitted that it could have entailed “collateral damage”.

This is while reports say MSF staff phoned military officials at NATO in Kabul and Washington after the attack, and bombs continued to rain down near the medical facility for nearly an hour, one official from the aid group said.

The UN human rights chief said the US airstrike that killed 19 people "may amount to a war crime."

Zeid Ra'ad al-Hussein said the attack on the medical center was "utterly tragic, inexcusable, and possibly even criminal."

According to a Press TV correspondent, Afghan President Ashraf Ghani strongly condemned the US airstrike in the northern city. He also offered his condolences to the families of victims and ordered local officials in Kunduz to thoroughly investigate the raid and send him their findings.

Kunduz has been witnessing heavy clashes between Afghan government forces and Taliban militants. At least 60 people have reportedly been killed and 400 injured over the past few days of fighting.