A Russian strike has hit a crowded market in the Ukrainian city of Kostiantynivka, killing at least 17 people, as the US secretary of state, Antony Blinken, was in Kyiv for an unannounced visit, his first for a year to the Ukrainian capital. Ukrainian officials said a further 32 people were wounded in the attack, one of Russia’s deadliest attacks in months, 12 miles (20km) from the frontlines in the Donetsk region of eastern Ukraine. Video of the aftermath showed fires raging in destroyed buildings and soldiers carrying body bags away from the scene. The Ukrainian prime minister, Denys Shmyhal, said a child was among those killed. “A regular market. Shops. A pharmacy. People who did nothing wrong. Many wounded,” the Ukrainian president, Volodymyr Zelenskiy, wrote in a post on Telegram. He called the strike “a terrorist attack” and said in a later press conference that it reflected the situation on the battlefield. “Whenever there are any positive advances by Ukrainian defence forces in that direction, Russians always target civilian people and civilian objects.” Russia also targeted Kyiv with ballistic missiles in the hours prior to Blinken’s arrival, with loud booms audible in the Ukrainian capital shortly before 6am, as his train was approaching. “It was clearly meant as a greeting to Blinken,” Mykhailo Podolyak, a key adviser to Zelenskiy, told the Guardian. “Russia is constantly showing that it will not abide by any rules,” Podolyak added. He said Russia had used Iskander missiles in the Kyiv attack, which was thwarted by Ukrainian air defences. Falling debris damaged building but there were no casualties, officials said. Blinken met his Ukrainian counterpart, Dmytro Kuleba, in Kyiv and held discussions with Zelenskiy. The two-day visit will include an overnight stay in the Ukrainian capital. While Blinken was in Kyiv, the US announced a new package of military assistance, including $100m (£80m) in financing for Ukraine’s long-term requirements and $175m in arms and ammunition drawn from US stockpiles, which included depleted uranium shells for the US M1 Abrams tanks that are due to be delivered by the end of this year. Depleted uranium shells are effective in piercing armour, but concerns have been raised over the incidence of cancer and birth defects in areas where they have been used. Because they have not definitively been identified as the cause, they are not banned under international law. The arms package also included components for air defence systems, guided multiple launch rocket systems, 155mm artillery and 105mm artillery ammunition. “I’m here in large part at the behest of President Biden to reaffirm our commitment to stand with you – to stand with you to help ensure that you succeed militarily in dealing with the aggression, but also to stand with you to make sure that your efforts to build a strong economy and a strong democracy succeed,” Blinken said, in remarks before a meeting with Shmyhal. The visit comes shortly after Zelenskiy fired his defence minister, and as Ukraine’s military counteroffensive grinds on in the south-east of the country. On Wednesday Ukraine’s parliament approved the appointment of Rustem Umerov as the new defence minister. He replaces Oleksii Reznikov, who was sacked after a number of corruption scandals linked to the defence ministry. Reznikov is tipped to become ambassador to Britain. Umerov was tasked with negotiations with Russia in the early stages of the war, before heading the state property fund, Ukraine’s main privatisation agency. “He has an impeccable reputation, and all political circles respect him,” said Podolyak. “He’s a consensus candidate, which is important.” In a statement posted to Facebook, Umerov promised to do “everything possible and impossible” to bring about Ukraine’s victory, saying: “42 million Ukrainians stand behind every solider. Behind every soldier is a ministry that will do everything to protect and provide for all our people.” Unnamed western officials have criticised the speed and tactics of Ukraine’s counteroffensive, which has irritated Ukrainian officials. The offensive has proceeded more slowly than expected, partly due to the extensive fortifications and minefields that Russian forces have built to defend their lines. “I understand that the further away you are from the war, sitting in your office, the better you understand the war, and if you’re 10,000km away then it’s the best place to understand what is happening,” said Podolyak, in a sarcastic aside. He criticised western officials who saw the war as “arrows on a map” rather than in terms of human lives, but said in recent months there had been an increased understanding of the task Ukraine faced in pushing through Russian lines. One senior western official said in a briefing to journalists on Wednesday that Ukraine was making “incremental but methodical progress” on parts of the southern and eastern fronts but accepted it was “slower than expected a couple of months ago”. This was due to the heavier than expected minefield belt laid by the Russians on the frontline, at times forcing Ukrainian soldiers to dismount and “crawl on their bellies to get through”, meaning that the pace of advance has been at best a few hundred metres a day. An unnamed US official told Reuters that Blinken wanted to get a first-hand assessment of the counteroffensive during the trip. “What’s most important is that we get a real assessment from the Ukrainians themselves,” the official said. “We want to see, hear how they intend to push forward in the coming weeks.”