Russian protesters laid down in the street in an anti-war demonstration recreating the Bucha massacre.
Hundreds of dead civilians were found in the city of Bucha, with growing evidence suggesting horrific barbarism -including the rape of women and children raped then shot dead.
An unnamed artist from Moscow is believed to have started the demos by laying facedown in the streets of the Russian capital.
He was pictured on the ground wearing a brown jacket and black hoodie with his hands tied behind his back.
It comes as Ukrainian officials have vowed to hunt down the "butchers of Bucha" after the dead civilians were discovered.
Kyiv intelligence sources have named Lt Colonel Azatbek Omurbekov - who leads the 64th Separate Motorised Rifle Brigade which occupied the region - as the commander in the area.
Zelensky has warned that worse evidence of mass killings of civilians by Moscow will emerge as the Russian president repositions his troops to the south-east.
It will be his first address to the Security Council, whose presidency is held by the UK, with members including Russia and China.
The Ukrainian leader accused Moscow of committing "real genocide", as he appeared visibly emotional, flanked by his soldiers and wearing a bullet-proof vest.
Ihor Zhovkva, deputy head of the office of the President of Ukraine, said Mr Zelensky "will give all the evidence" to the international community at the Security Council meeting.
"If these awful atrocities will not change the agenda of all the world, what will change?" the adviser asked on BBC Radio 4's Today programme.
Mr Zhovkva said Ukraine needs "additional weapons", including tanks and missiles, to "liberate more cities" from Russia control.
Dame Barbara Woodward, Britain's UN ambassador, called images coming from Bucha "harrowing, appalling, probable evidence of war crimes and possibly a genocide".
She cited hundreds of bodies being dumped in the streets or in mass graves and allegations of rape.
Ukrainian reporter Evgeny Spirin said: “Some of the killed children had their arms tied up. Children…. They were tying up children. There were shot dogs."
