Nato countries have not delivered what they promised to Ukraine in time, which has benefited Russia on the frontline, Jens Stoltenberg has said. “Serious delays in support have meant serious consequences on the battlefield” for Ukraine, the Nato secretary general said in Kyiv while meeting the Ukrainian president, Volodymyr Zelenskiy. Ukrainian officials say Russia is assembling forces for a major summer offensive, even if its troops are making only incremental gains at the moment. “The lack of ammunition has allowed the Russians to push forward along the front line,” Stoltenberg said. “Lack of air defence has made it possible for more Russian missiles to hit their targets, and the lack of deep strike capabilities has made it possible for the Russians to concentrate more forces.” Zelenskiy said new western supplies have started arriving, but slowly. “This process must be speeded up,” he said. At least four people were killed and 32 injured in a Russian missile strike on residential buildings and “civil infrastructure” in Odesa on Monday, said regional officials. The attack hit a private law academy situated in a popular seafront park in the southern Ukrainian port city. A turreted Gothic-style building known as the “Harry Potter castle” was seen in flames after the strike. Ukrainian navy spokesperson Dmytro Pletenchuk said the strike was conducted by an Iskander-M ballistic missile with a cluster warhead. “Monsters. Beasts. Savages. Scum. I don’t know what else to say,” said the Odesa mayor, Hennadii Trukhanov. Debris showed that an North Korean Hwasong-11 ballistic missile hit Kharkiv on 2 January, UN sanctions monitors have told a security council committee in a report seen by Reuters. The missile was most likely illegally supplied to Russia, they conclude. North Korea is accused of developing such weapons and supplying them to Russia despite being under UN sanctions for its ballistic missile and nuclear programmes since 2006. Ukraine’s allies have accused North Korea of transferring weapons to Russia for use against Ukraine in violation of an arms embargo. The US has accused Russia of launching North Korean-supplied ballistic missiles against Ukraine on at least nine occasions. Russia in March vetoed the renewal of sanctions monitoring against North Korea’s nuclear and ballistic missile programmes. Away from the frontline, Polish farmers have lifted blockades at border crossings with Ukraine, officials said on Monday, ending a two-month protest over farm imports and alleged unfair competition. “The traffic through all the border crossings [with Ukraine] is possible,” said Michal Derus, a tax administration spokesman in Poland’s Lublin region after farmers ended the last blockade at the Hrebenne border crossing. “All trucks are allowed to pass as long as they are not carrying sanctioned goods,” Derus added, referring to the grain imports from Ukraine that Poland imposed a temporary embargo on. German prosecutors are investigating after a Russian citizen was arrested on suspicion of stabbing two Ukrainian soldiers to death. The soldiers – who had been convalescing in southern Germany – were found with serious stab wounds outside a shopping centre in the Bavarian town of Murnau am See on Sunday, according to police. One of them, aged 36, died at the scene, while the other, 23, died in hospital. A 57-year-old Russian citizen was arrested in his home on suspicion of murder, police said. The prosecutor general’s office in Munich said it had since taken over the case and was not able to rule out that the killings were politically motivated. Sophie, Duchess of Edinburgh, on Monday became the first British royal to visit Ukraine since Russia’s full-scale invasion. The British foreign ministry said she met survivors of sexual violence and torture, as well as women displaced by the war, and children who were deported to Russia before recently being returned. “It’s true that women and girls pay the highest price in terms of human cost … Rape is used to demean, to degrade and to destroy, and we have to get better at trying to prevent that from happening,” Sophie said. The Russian army in Ukraine has been accused of numerous incidents of rape and sexual violence