A suspected US air strike on a hospital in the Afghan city of Kunduz that killed nine MSF staff on Saturday was "inexcusable" and possibly criminal, UN rights chief Zeid Ra'ad Al Hussein said.

Zeid called for a full and transparent investigation, noting that, "if established as deliberate in a court of law, an air strike on a hospital may amount to a war crime."

“This event is utterly tragic, inexcusable and possibly even criminal,” Zeid said in a statement.