Germany's Foreign Minister said on Sunday Russia must pay for its "war crimes" in the Ukrainian town of Bucha just outside the capital in the form of more severe sanctions, denouncing Russian President Vladimir Putin's "uninhibited violence".
The mayor of Bucha said on Saturday that 300 residents had been killed during a month-long occupation by the Russian army. Victims were seen by Reuters in a mass grave and still lying on the streets.
"The images from Bucha are unbearable, Putin's uninhibited violence is extinguishing innocent families and knows no boundaries," Baerbock wrote on Twitter.
"Those responsible for these war crimes must be made accountable. We will tighten the sanctions against Russia and will assist Ukraine even more in defending itself."
The Russian defence ministry in Moscow did not immediately reply to a request for comment when asked on Sunday about bodies found in Bucha.
Russia has previously denied targeting civilians and rejected allegations of war crimes in what it calls a "special military operation" in Ukraine.
In a statement on Sunday German Chancellor Olaf Scholz called for international organisations such as the International Committee of the Red Cross (ICRC) to be allowed access to the affected areas to independently document what he described as atrocities.
Scholz also called on Russia to finally agree to a ceasefire and put a stop to this "terrible, meaningless and unjustifiable war".
Germany was preparing the sanctions in conjunction with partners in the European Union, Economy Minister Robert Habeck was quoted as saying by German newspaper Bild.
The EU is working on further sanctions on Russia but any additional measures will not affect the energy sector, the bloc's Economic Commissioner Paolo Gentiloni said on Saturday.
Berlin has so far resisted growing calls to impose an embargo on Russian energy saying its economy and that of other European countries are too dependent still on Russian imports.
(Reporting by Kerstin Doerr; Writing by Sarah Marsh; Editing by Raissa Kasolowsky)