Ukraine's president has warned that Russia's blockade of ports in southern Ukraine could prevent the country from exporting 75 million tons of grain by autumn.

Volodymyr Zelenskyy told reporters in Kyiv on Monday that roughly 22 to 25 million tons of grain have already been blocked from export. He suggested that the amount may increase to 75 million tons by autumn.

Zelenskyy said Ukraine needs a "safe corridor for ships," and that his government has talked with Britain and Turkey on methods to ensure exports.

In Moscow, President Vladimir Putin has denied Ukraine's claim that Russia is blocking shipments. He spoke about the issue last Friday on state-run TV.

Putin said Russia will ensure a problem-free exit from ports on the Sea of Azov, which it controls, and guarantee the peaceful passage of vessels to international waters. He added, "The problem of shipping grain out of Ukraine does not really exist."

Ukraine is a major grain exporter, and the lack of shipments due to the Russia's invasion is raising fears of a global shortage.

Russian Foreign Minister Sergey Lavrov is scheduled to visit Turkey and meet his counterpart on Wednesday. Attention is focused on whether progress can be achieved on the issue of setting up a safe shipping corridor.