United Nations Secretary-General Antonio Guterres on Wednesday called the six-month anniversary of the start of Russia's war in Ukraine a "sad and tragic milestone."

Guterres made the comments during a special meeting of the UN Security Council in New York to mark the anniversary of Russia's invasion of its neighbor on February 24.

The UN chief described the six months of conflict as "devastating."

"The consequences of this senseless war are being felt far beyond Ukraine," said Guterres, referring to its impact on food and fuel prices.

"If we don't stabilize the fertilizer market in 2022, there simply will not be enough food in 2023," the secretary-general warned.

Guterres said he remained "gravely concerned" about military activity around the Zaporizhzhia nuclear plant in southern Ukraine, Europe's largest atomic power plant.

"The warning lights are flashing," he said.

"Any further escalation of the situation could lead to self-destruction. The security of the plant must be ensured, and the plant must be re-established as purely civilian infrastructure," he added.

The plant is occupied by Russian troops and threatened by shelling, which Moscow blames on Kyiv.

Ukrainian President Volodymyr Zelensky, addressing the meeting via video-link, told the UN that Russia "should unconditionally stop nuclear blackmail" and "completely withdraw" from the plant.

"Europe and neighboring regions face the threat of the radiation pollution. This is a fact," Zelensky, told the session, which had been requested by the United States, France and Britain.

Russia's ambassador to the UN, Vassily Nebenzia, objected to Zelensky being allowed to speak.

He said he was not opposed to the Ukrainian leader's participation, but to the fact that he was not attending in person.

The 15-member council voted 13 to one in favor of allowing Zelensky to speak, with China abstaining.