Ukraine on June 6 threw what could be a major wrench in the works of a Turkey-mediated plan to open shipping corridors out of Ukrainian ports when Kyiv officials said it would take six months to clear the Black Sea coast of Russian and Ukrainian mines.

With fears mounting that a failure amid the war in Ukraine to ship vast amounts of the Ukrainian grain harvest to markets could cause a major global food crisis, Russia’s foreign minister, Sergey Lavrov, arrived in Ankara for talks on securing the corridors. Turkey’s defence minister, Hulusi Akar, at the same time said that Turkey was making progress with the UN, Russia and Ukraine on reopening ports faced by the Russian blockade in the Black Sea. Ships departing Ukrainian ports would be escorted by Turkish naval vessels under the proposal being discussed, with Turkish minesweeper vessels helping to clear shipping lanes of mines.

The plan was sounding increasingly promising until Markiyan Dmytrasevych, an adviser to Ukraine’s minister of agrarian policy and food, stepped into the discussion to state that, even should Moscow lifted its blockade, thousands of mines would remain floating around the port of Odesa, and elsewhere. He added that presently Ukraine was able to export a maximum of 2m tonnes of grain a month, as against 6m tonnes before the outbreak of the war, and that it would take until the end of the year to clear the mines.

“I think we reached the limit,” Dmytrasevych told participants at an International Grains Council conference, as cited by the Guardian. “The biggest amount we can export is about 2m tonnes a month.”

Russia and Ukraine supply around 40% of the wheat consumed in Africa, where prices have already risen by about 23%, according to the UN.

It is estimated that something around 20m tonnes of grain are stranded in silos around Odesa. The export of Ukrainian grain by road, rail and river through Ukraine’s Danube ports is severely constricted by capacity constraints and the different railway gauges used by countries along key export routes. The railways of Ukraine and Poland, for instance, use different gauges.

In addressing Turkey’s demining proposal, Ukraine has also expressed anxieties that it could leave Odesa and other key ports open to attack.

Volodymyr Zelenskiy, president of Ukraine, said in an interview with the Financial Times that he supported the Turkish initiative, but he would require assurances that Russian vessels would not be permitted to use the safe-passage corridors.

The Kremlin, meanwhile, has said that any ships wishing to enter the Ukrainian ports to load grain would need to be checked by the Russian military to ensure they were not carrying weapons.

At a UN security council meeting on June 6 in New York, European Council President Charles Michel accused Russia of using food supplies as “a stealth missile against developing countries” and of stealing grain from occupied Ukrainian territories. He talked of “cowardly” actions and “propaganda, pure and simple”. His remarks prompted the Russian ambassador to the UN, Vassily Nebenzia, to walk out.