Ukrainian President Volodymyr Zelenskiy said on Friday he would only support the idea of reopening Russian ammonia exports through Ukraine only if Moscow handed back prisoners of war, an idea the Russia quickly rejected.
In an interview, Zelenskiy told Reuters he had proposed the arrangement to the United Nations, which has suggested resuming Russian ammonia across Ukraine to ease a global shortage of fertiliser.
"I am against supplying ammonia from the Russian Federation through our territory. I would only do it in exchange for our prisoners. This is what I offered the UN," he said in an interview at his presidential office.
Kremlin spokesman Dmitry Peskov dismissed the idea, TASS news agency reported. "Are people and ammonia the same thing?" it cited him as saying.
The United Nations has proposed that ammonia gas owned by Russian fertiliser producer Uralchem be pumped by pipeline to the Ukrainian border, where it would be bought by the U.S.-based commodities trader Trammo.
The pipeline is designed to pump up to 2.5 million tonnes of ammonia per year from Russia's Volga region to Ukraine's Black Sea port of Pivdennyi, known as Yuzhny in Russian, near Odesa.
It was shut down after Russia sent its troops into Ukraine on Feb. 24.
Zelenskiy said that hundreds of Russian troops had been captured during Ukraine's lightning counteroffensive in northeast Ukraine's Kharkiv region.
He said, however, that Russia was holding more Ukrainian soldiers in custody than Ukraine had Russian POWs.
The fate of Ukrainian soldiers held by Russia, and in particular those captured after holding out for months in the Azovstal steelworks in the besieged city of Mariupol, is a highly sensitive issue in Ukraine.
Some of their relatives were huddled on Friday outside the government district in Kyiv where Zelenskiy's office is located, holding signs saying "Bring the Azovstal Heroes Home".