Volodymyr Zelenskiy warned that any attacks by Russia on the country’s independence day would be met with a powerful response as Ukraine prepared to mark 31 years since the end of Soviet rule. The Ukrainian president’s defiant message followed warnings from western and Ukrainian officials that Russia was preparing to once again attack the capital, Kyiv, on the date that also marks six months since the 24 February invasion. The US on Tuesday urged all its citizens to leave the country, saying it believed Russia would target civilian and government infrastructure in the next few days. Kyiv authorities banned mass gatherings in the capital to mark Ukraine’s 1991 independence from the Soviet Union. Instead of the traditional parade down Kyiv’s main street, authorities have lined the road with captured and destroyed Russian military equipment. The car-bomb killing of the daughter of a prominent ultra-nationalist Russian ideologue at the weekend, which Russia has blamed on Ukraine, has also added to fears of reprisals. Darya Dugina’s funeral was held in Moscow on Tuesday, at which her father, Alexander Dugin, said that only victory in Ukraine could justify the price that she paid. Zelenskiy said he had information from Ukraine’s intelligence services and international partners that there was an increased threat, but stressed that the threat from Russia had remained daily and constant since 24 February. He told a news conference in Kyiv that Ukraine would not agree to any proposal to freeze current frontlines in order to “calm” Moscow, which now controls about 22% of Ukraine, including Crimea. On Wednesday, the US will announce a fresh security assistance package for Ukraine of about $3bn (£2.5bn), officials said, to coincide with Ukraine’s independence day and to equip the country for a war of attrition fought primarily in eastern and southern Ukraine. “If the world shows fatigue with the war in Ukraine, it will be a big threat to the whole world,” Zelenskiy told an online conference on Crimea attended by representatives of 60 states. He also vowed to return Crimea to Ukraine, saying that it would become part of the EU, along with the rest of the country. “It all began with Crimea, and it will end with Crimea,” said Zelenskiy. The outgoing British prime minister, Boris Johnson, who spoke via video link at the conference, said Britain would never recognise Russia’s annexation of Crimea or any other parts of Ukrainian territory. “In the face of Putin’s assault we must continue to give our Ukrainian friends all the military, humanitarian, economic and diplomatic support that they need until Russia ends this hideous war and withdraws its forces from the entirety of Ukraine,” Johnson said. The president of Turkey, Recep Tayyip Erdoğan, also spoke at the conference, saying that Crimea should be returned to Ukraine. Erdoğan, who helped negotiate the recent grain deal, has been maintaining ties with Zelenskiy and Russia’s president, Vladimir Putin. Crimea has become the focus of attention over the last two weeks after a series of explosions at Russian military bases on the peninsula. Ukraine has not claimed responsibility for the attacks. But Ukraine’s defence ministry has worked to foster the impression that Ukraine was involved, publishing a video on Twitter that warned Russians not to visit Crimea “unless they want an unpleasantly hot summer break”. Several media reports, including one by CNN, say they have confirmed Ukraine was responsible, citing anonymous Ukrainian officials. On the eve of Ukraine’s independence day, there were reports of the sounds of explosions in Sevastopol, at the south of Crimea. Russia’s occupying authorities in the city reported that air defence systems had downed a Ukrainian drone over the sea. Meanwhile, Dnipro’s mayor, Borys Filatov, said Russia had launched a rocket at the central Ukrainian city on Tuesday morning. “Please stay in the [bomb] shelters,” Filatov wrote on his Telegram channel. He later wrote that the rocket had landed on private houses and there was no nearby military target. Ukraine’s defence ministry has advised Ukrainians to be especially careful on independence day, citing the threat of missile attacks and “provocations” from Russia. “Russia and the Putin regime attacked the independence of Ukraine and independent Ukraine. They are really obsessed with dates and symbols, so it would be logical to be on the lookout and be prepared for independence day to be attacked,” Andriy Yusov, the head of the ministry’s intelligence directorate, said on Ukrainian state TV. Kyiv is far from the frontlines and has rarely been hit by Russian missiles since Ukraine repelled a ground offensive to seize the capital in March, but some Kyiv restaurants have been closing early this week because of the perceived increased threat. The head of Ukraine’s security and defence council, Oleksiy Danilov, said he expected Russia’s security services to stage a series of terrorist attacks in Russian cities resulting in civilian losses, in an attempt to reignite domestic support for the war. Danilov said he believed the killing of Dugina was the first such attack. After the attack, which Russian security services blamed on Ukraine, a host of prominent pro-Putin figures called for revenge. Ukraine denies responsibility. Russia’s foreign minister, Sergei Lavrov, vowed “no mercy” for the killers. A spokesperson for the UN rights office said it was concerned about Russian attempts to try Ukrainian prisoners of war in the coming days, saying the process could amount to a war crime. “We are very concerned about the manner in which this is being done. There are pictures in the media of cages being built in Mariupol’s philharmonic hall, really massive cages and apparently the idea is to restrain the prisoners,” Ravina Shamdasani told a UN briefing. “This is not acceptable, this is humiliating.” Wilfully depriving a prisoner of war to the right to a fair trial amounted to a war crime by Russia, she added. Zelenskiy has said that if Russia puts the prisoners on trial it will eliminate the possibility of talks with Moscow. Ukraine’s human rights ombudsman, Dmytro Lubinets, called on the UN and the International Committee of the Red Cross to intervene and prevent the trial.