Ukraine is bracing itself for an intensification of Russian missile attacks to coincide with its independence day on Wednesday in the aftermath of the car-bomb killing of the daughter of an ultranationalist Russian ideologue. The country’s military warned that Russia had put five cruise missile-bearing warships and submarines out in the Black Sea and that Moscow was positioning air defence systems in Belarus. Large gatherings have been banned in Kyiv for four days from Monday. Overnight on Saturday, Ukraine’s president Volodymyr Zelenskiy had warned that “Russia may try to do something particularly nasty, something particularly cruel” this week as the country celebrates its 31st anniversary of independence. The country’s armed forces also warned on Sunday night that Russia had closed the airspace in the Russian border regions of Lipetsk, Voronezh and regions between 22 and 25 August. Tensions between the two warring countries were at risk of heightening further after the killing of Darya Dugina, whose father is the Russian political commentator Alexander Dugin, on the outskirts of Moscow on Saturday night. Investigations into the killing were continuing, although some Russian hawks tried – without evidence – to blame Ukraine, which in turn denied any involvement in the attack, saying it was “not a terrorist state”. On Sunday night, a former member of Russia’s Duma now based in Kyiv who was expelled for anti-Kremlin activities claimed that a previously unknown group of Russian partisans were behind the attack. Ilya Ponomarev claimed the deadly explosion was the work of the National Republican Army, which he said was an underground group working inside Russia dedicated to overthrowing the Putin regime. “This action, like many other partisan actions carried out on the territory of Russia in recent months, was carried out by the National Republican Army (NRA),” Ponomarev said, speaking on his YouTube channel. The Guardian has not verified the authenticity of the claims. Concern about whether Russia would step up its attacks around Ukraine’s independence day had been in the air for some time and predated the Moscow car bomb. But it could be used as an additional pretext by Moscow. Prominent Russian hawks blaming Kyiv for the car bomb called it “an assassination attempt” and demanded that the Kremlin respond by targeting government officials in Kyiv. “Decision-making centres!! Decision-making centres!!!” wrote Margarita Simonyan, the editor-in-chief of the state-funded RT television station, reposting a call to bomb the headquarters of the Ukrainian SBU intelligence agency. Maria Zakharova, a spokesperson for the Russian foreign ministry, said that if a Ukrainian link was confirmed and was verified by the competent authorities, “then we should talk about the policy of state terrorism implemented by the Kyiv regime”. If the car bombing is definitively tied to the war, it would mark the first time since February that the violence unleashed on Ukraine has reached the Russian capital, touching the family of a Kremlin ally near one of Moscow’s most exclusive districts. Kyiv strongly denied the allegations. “Ukraine has absolutely nothing to do with this, because we are not a criminal state like Russia, or a terrorist one at that,” Mykhailo Podolyak, an adviser to Zelenskiy, said in remarks broadcast on television. Keir Giles, a Russia expert at the Chatham House thinktank, said it was unclear whether Ponomarev’s claims about the NRA were true: “How the Kremlin will respond depends on whether this is a genuine resistance movement or a Russia-style complex conspiracy of smoke and mirrors – and we may not know for some time yet.” The blast occurred shortly after Dugina left the Tradition cultural festival at an estate where her father had given a lecture. The two were expected to leave together, but instead got into different cars, a friend said. Five minutes later, a bomb exploded in the car Dugina was driving, killing her instantly. Witnesses said debris was thrown all over the road as the car was engulfed in flames before crashing into a fence. Dugin is known for developing an extreme rightwing view of Russia’s place in the world and had previously advocated violence against Ukraine, while his daughter held similar views. He has been described as a “Russian fascist” and is a well-known conspiracy theorist. Some claim he helped shape the Russian president’s expansionist foreign policy. But the influence of Dugin over Putin remains a subject for speculation, with many insiders saying his sway over the Kremlin was minimal. Investigators believed the bombing was “premeditated and of a contract nature”, said Alexander Bastrykin, the head of the investigative committee, the main federal investigating authority in Russia. Andrey Krasnov, a friend of Dugina and the head of the Russian Horizon social movement, confirmed the reports, according to the news agency Tass. He said the bomb could have been intended for her father. “This was the father’s vehicle. Darya was driving another car, but she took his car today, while Alexander went a different way. He returned, he was at the site of the tragedy. As far as I understand, Alexander or probably they together were the target,” Krasnov said. However, the independent Russian news agency Agentstvo reported that leaked government databases showed the car was registered to Darya, not her father. Footage on social media appeared to show him at the scene in a state of distress. Investigators said they had opened a murder case and would be carrying out forensic examinations to try to determine what happened. They said they were considering “all versions” when it came to working out who was responsible.