UN humanitarian chief Martin Griffiths said Thursday during a visit to the town of Bucha outside the Ukrainian capital Kyiv that investigators would probe civilian deaths uncovered after Russian troops withdrew."The world is already deeply shocked," Griffiths said in the town that was strewn with bodies after Moscow's forces pulled out, adding that, "the next step is conducting investigations."Griffiths arrived in Bucha around 1300 GMT, accompanied by Amin Awad, the UN's coordinator on the Ukraine crisis, for a three-hour visit that included a stop at the site of a mass grave that Ukrainians had dug near a church.His trip came a day after he visited Moscow, where he met with officials to discuss the humanitarian situation in Ukraine, more than a month into the Russian invasion.Evidence of civilian killings in Bucha and other towns around Kyiv which Ukraine has blamed on Russian troops, allegations denied by Moscow have shocked the world and triggered calls for new sanctions on Moscow.Russia's President Vladimir Putin has denied any responsibility for civilian deaths, accusing Ukrainian authorities of "crude and cynical provocations" in Bucha.