Ukraine’s military intelligence has warned that Russian forces may be preparing to stage a “provocation” at a nuclear power plant they control, as the UN secretary general, António Guterres, called for an urgent withdrawal of military forces and equipment from the site. Guterres, on his second visit to Ukraine since the Russian invasion, joined the Ukrainian president, Volodymyr Zelenskiy, and the Turkish president, Recep Tayyip Erdoğan, for meetings and then a press conference in the western city of Lviv. “We are worried. We don’t want another Chernobyl,” Erdoğan said. It was the first visit to Ukraine by Turkey’s leader, who has been a key intermediary in negotiations with Russia. Zelenskiy said he agreed with Guterres on a framework for a visit by the International Atomic Energy Agency watchdog to inspect the Zaporizhzhia nuclear power plant, the largest in Europe. It was taken over by Russian forces in March but is still being run by Ukrainians. The UN chief called on Russian forces to leave with their military equipment, amid fears that fighting around the site could lead to a deadly disaster. Moscow and Kyiv have traded accusations of shelling the site. “The facility must not be used as part of any military operation. Instead, agreement is urgently needed to re-establish Zaporizhzhia’s purely civilian infrastructure and to ensure the safety of the area,” Guterres said. Video footage shared online by a New York Times reporter showed at least five apparently military trucks parked inside the plant’s engine room near the turbo generator. In the hours before the international summit in western Ukraine, Russia announced it had deployed warplanes armed with hypersonic missiles to its Kaliningrad region, an enclave on the Baltic Sea that borders the EU and Nato members Poland and Lithuania. The commander of its Black Sea fleet has also been replaced, the Russian RIA news agency said, in one of the most high-profile military sackings since the invasion. It came after a series of humiliations for the fleet, including the sinking of its flagship Moskva cruiser and an attack on a key airbase in Crimea. Inside Ukraine, Russian forces stepped up attacks on Kharkiv, the country’s second largest city, ahead of the summit in Lviv. In attacks overnight and early on Thursday morning, at least 11 people were killed and more than 40 injured and a residential block was destroyed. Ukraine’s defence intelligence agency said it was concerned that Russia had plans to stage an incident at the plant on Friday, and had information that staff with Russia’s Rosatom nuclear company had left the site. Russian state media had already accused Ukraine of planning a “provocation” at the plant to coincide with the UN leader’s trip, raising fears that Russia’s military could be planning a “false-flag attack”. When Guterres travelled to Kyiv in April, Moscow carried out an airstrike on the city. On Wednesday, Ukraine’s interior minister, Denys Monastyrsky, said Ukraine must “prepare for all scenarios”, during a drill for emergency workers in Zaporizhzhia. On Wednesday, the Nato secretary general, Jens Stoltenberg, warned Russia’s seizure of the plant had “raised the risk of a nuclear accident or incident” and accused Moscow of being “reckless” by using the area as a staging platform to launch artillery attacks on Ukrainian forces. Russia said it may shut down the plant, claiming backup support systems had been damaged in strikes. Igor Kirillov, the head of the radioactive, chemical and biological defence force, said if there was an accident at the site, radioactive material would cover Poland, Germany and Slovenia. Ukraine’s hydrometeorological institute also warned of contamination spreading across Europe, a BBC journalist reported. Two issues are causing deepening anxiety about the situation at the Zaporizhzhia plant. International nuclear safety officials have become concerned over the lack of spare parts, access for routine maintenance of the reactors, and contact with staff, all of which have been disrupted by the conflict. A second issue is shelling around the plant. According to Energoatom, Ukraine’s nuclear authority, the impacts from Grad missiles earlier this month were close to the spent fuel storage area, with the plant’s operator claiming Russian troops “aimed specifically” at the containers, despite the Russian military’s presence at the site. Russia accuses Ukraine of carrying out the shelling. On Friday, Guterres will travel to the Black Sea port of Odesa, a crucial gateway for Ukrainian grain to reach the rest of the world. He will then continue to Turkey to visit the Joint Coordination Centre, the body tasked with overseeing the accord. Ukraine’s fields feed hundreds of millions of people worldwide, so the abrupt halt to shipments has pushed up global grain prices at a time when famine is already threatening east Africa. The UN last month brokered an agreement to let shipments restart. So far, 24 ships have left Ukraine’s Black Sea ports, a monitoring group said. Kyiv has a backlog of 18m tonnes of grain from last year’s harvest, even as it starts bringing in the 2022 crop. It hopes to soon raise exports to 3m tonnes a month, easing world prices and clearing storage space for new grain. It will be six months on 24 August since the start of the invasion – which Russia calls a “special military operation” – and several UN security council members, including the US, Britain, the Republic of Ireland and Norway, have called for a meeting on that date. Kyiv is expected to launch a counteroffensive in southern Ukraine in the coming weeks and has carried out spectacular attacks deep inside Russian-held territory, including on an airbase in Crimea. But despite shipments of western weapons and ammunition, Ukraine is still struggling against heavy Russian artillery bombardment along the eastern front. The Ukrainian presidential adviser Oleksiy Arestovych said in a video on Wednesday that the war had reached a “strategic deadlock”. “Russian forces have achieved only minimal advances, and in some cases we have advanced, since last month,” he said.