WASHINGTON — The United States expressed outrage at what it initially assessed to be a deliberate Syrian regime airstrike on a Doctors Without Borders-affiliated hospital in Aleppo that killed dozens of people, and the United Nations has warned of a catastrophe if the United States and Russia don’t quickly restore Syria’s partial cease-fire that has badly degraded in Syria’s largest city in the past week.

"We are outraged by yesterday’s airstrikes in Aleppo on the al-Quds hospital … which killed dozens of people, including children, patients and medical personnel," Secretary of State John Kerry said in a statement April 28.

“While we are still trying to gather the facts surrounding the circumstances of this attack, it appears to have been a deliberate strike on a known medical facility and follows the Assad regime's appalling record of striking such facilities and first responders," Kerry continued. "The United Nations today assessed the situation in Aleppo to be catastrophic … Russia has an urgent responsibility to press the regime to fulfill its commitments."

The rapidly escalating violence in Syria — which in the past 48 hours has been killing one Syrian every 25 minutes, UN special envoy for Syria Staffan de Mistura said April 28 — came as US officials said they were engaging intensively with Russian counterparts on how to restore the Syria cease-fire, but were oblique about at what level those discussions were taking place. US officials also acknowledged that Syrian opposition groups ostensibly abiding by the cessation were still "intermingling" with al-Qaeda-linked Jabhat al-Nusra militants in the wider Aleppo area, making delineating no-go areas more difficult.