The US secretary of state, Antony Blinken, arrived in Kyiv on Tuesday on his first visit to Ukraine since a major US aid package was passed last month. Blinken, who arrived by train from Poland in an unannounced visit, met with Ukraine’s president, Volodymyr Zelenskiy. “Some of it has already arrived and more of it will be arriving,” said Blinken of the US aid. “And that’s going to make a real difference against the ongoing Russian aggression on the battlefield.” Zelenskiy described the US aid as crucial, and thanked Blinken, but also said Ukraine desperately needed two more air defence systems to protect the city of Kharkiv, which has been hit repeatedly by Russian strikes in recent weeks. Blinken joined band 19.99 on stage at Barman Dictat, picking up a red guitar to play Neil Young’s Rockin’ in the Free World. “Your soldiers, your citizens – particularly in the north-east, in Kharkiv – are suffering tremendously. But they need to know, you need to know, the United States is with you, so much of the world is with you and they’re fighting not just for a free Ukraine, but for the free world. And the free world is with you, too,” Blinken said before playing the song. Ukraine’s military said its forces pulled back to new positions in two areas of the north-eastern Kharkiv region where Moscow is pressing an offensive, and warned of a Russian force buildup to the north near the Sumy region. Russia said on Tuesday it had taken a 10th border village, Buhruvatka, in Kharkiv region. The police chief in Vovchansk, a town 5km (three miles) from the border that has been the target of one of the main Russian thrusts, reported exchanges of fire in the north of the town. Russian strikes on residential areas in the centre of Kharkiv city injured 20 people on Tuesday, officials said. Ukrainian grid operator Ukrenergo said on Tuesday that power shortages caused by damage from Russian strikes had prompted controlled countrywide cuts from 9pm to midnight. “The reason is a significant shortage of electricity in the system as a result of Russian shelling as well as increased consumption because of cold weather,” Ukrenergo said. The Russian president, Vladimir Putin, will visit China on 16-17 May, Chinese state media reported. Joe Biden has signed legislation broadly supported in Congress that prohibits any imports of Russian uranium into the US from 12 August. Russia provides about 20-30% percent of the enriched uranium used in the US and Europe and 44% globally, according to the US energy department. The legislation will release $2.72bn in funding for the energy department to invest in uranium enrichment inside the US. Russia has put its Bulava intercontinental ballistic missile into service, the Tass state news agency reported on Tuesday, citing the system’s chief designer.