The UN has said that Ukrainians are enduring a "living hell", amid sieges and bombardments by Russian forces.
Secretary-General Antonio Guterres said the war in Ukraine was not only causing untold misery for Ukraine but also affecting people around the world.
"The Ukrainian people are enduring a living hell – and the reverberations are being felt worldwide with skyrocketing food, energy and fertiliser prices threatening to spiral into a global hunger crisis," the UN chief said.
He also said the war was "unwinnable" and that prolonging the war would only prolong the suffering of millions of people in Ukraine.
"What I said from this podium almost one month ago should be even more evident today. By any measure - by even the shrewdest calculation - it is time to stop the fighting and give peace a chance."
It comes as US President Joe Biden warned on Monday evening that a cornered Vladimir Putin could order Russian forces to use chemical or biological weapons.
Russia has already falsely claimed to have discovered a bioweapons laboratory in Ukraine and that Kyiv has chemical weapons stockpiles.
Biden said these claims indicate that a "cornered" Putin might be prepared to launch a "false flag operation" and blame Ukraine.
Foreign Minister Jean-Yves Le Drian has also said that if chemical weapons were used in Ukraine, Russia would be to blame.