An air strike on a hospital in the city of Aleppo that killed dozens of people was probably the work of Syrian government forces, a spokesman for the German government said on Friday.

A U.S. official has also said the attack on Wednesday night appeared to be solely the work of the Syrian government. Syria’s military has denied its warplanes targeted the hospital.

German government spokesman Steffen Seibert told a news conference the destruction was targeted and therefore constituted the “murder of a huge number of civilians”.

“The available information suggests that this attack can, with some degree of probability, be traced back to the troops of (President Bashar al-Assad’s) regime,” Seibert said, adding that it was a “blatant violation of humanitarian law”.

The German government warned that the escalation of fighting in Aleppo and elsewhere threatened to undermine peace talks in Geneva.

“That must be avoided,” said Seibert, adding that Russia had a duty to prevent the ceasefire and the political process from failing.

The Geneva talks aim to end a war that has created the world’s worst refugee crisis, allowed the rise of Islamic State and drawn in regional and major powers, but a truce intended to allow negotiations to take place has collapsed.

German Foreign Minister Frank-Walter Steinmeier said in a statement on Friday: “The Syrian government must decide – does it want to take part in negotiations seriously or does it want to continue to reduce its own country to rubble?”