President Joe Biden called Russian President Vladimir Putin a "war criminal" on Monday after sickening images of dead civilian bodies filling mass graves and littering the streets of the Ukrainian city Bucha surfaced over the weekend. "We have to gather the information [to prove Putin is committing war crimes], we have to continue to provide Ukraine with the weapons they need to continue to fight and we have to get all the details so this can be an actual – have a war crime trial," Biden told the press. Ukrainian President Volodymyr Zelensky visited the ruins of Bucha on Monday. He urged the media to visit Bucha to tell the story of what had happened to the rest of the world. “Ordinary residents of an ordinary city near Kyiv,” Zelensky said in an address to the Romanian parliament. “Their hands were tied behind their backs, they were shot in the back of the head or in the eye, killed just in the streets. Civilian vehicles were crushed by military equipment. Vehicles with people! They raped women and girls.” Zelensky warned that the released images did not show the worst of what happened. World leaders further condemned Russia and contemplated even harsher sanctions. French President Emmanuel Macron said he is considering issuing additional sanctions including banning Russian oil imports to the European Union while calling the Bucha photos "unbearable." Germany has signaled willingness to cut off the importation of Russian gas. The country has been reluctant of doing so as over half of its gas is sourced from Russia. “We will do everything to ensure that those who have perpetrated these war crimes do not go unpunished," Spanish Prime Minister Pedro Sanchez said Monday, referring to "alleged cases of [crimes against] humanity, war crimes and — why not say it too — genocide." The U.S. has stopped short of calling the Russia-Ukraine killings "genocide." National Security Adviser Jake Sullivan said that white it is clear war crimes have been committed, so far there is no evidence of "systematic" killings. The U.S. is set to implement additional sanctions against Russia this week.