The Ukrainian president made a rare trip out of his country Wednesday, daring to visit Britain in a bid for more advanced weapons as Kyiv braces for an expected Russian offensive and hatches its own plans to retake land held by Moscow’s forces.

President Zelensky arrived on a Royal Air Force plane at London Stansted airport north of the U.K. capital. Prime Minister Sunak greeted him on the tarmac, tweeting a photo of him embracing the Ukrainian leader.

“The United Kingdom was one of the first to come to Ukraine’s aid. And today I’m in London to personally thank the British people for their support,” Mr. Zelensky said on Instagram.

A large convoy of vehicles left the airport and headed straight to Downing Street in central London. Both leaders posed briefly for photos in front of the famous black no. 10 door that leads into the U.K. prime minister’s residence.

Messrs. Zelensky and Sunak will hold talks before heading to Parliament, where the Ukrainian president will address lawmakers. It is his first trip to the U.K. since Russia’s invasion began nearly a year ago and only his second confirmed journey outside Ukraine during the war. 

Mr. Zelensky will also meet with King Charles III and U.K. military chiefs during his visit. Whether he will also see a former British prime minister, Boris Johnson, was not immediately clear. The two leaders struck up a much publicized rapport while Mr. Johnson, one of Ukraine’s most vocal supporters, still occupied 10 Downing Street.

Britain is one of the biggest military backers of Ukraine and has sent the country the equivalent of  more than $2.5 billion in weapons and equipment.

The visit comes as Mr. Sunak announced that Britain will train Ukrainian pilots on “NATO-standard fighter jets.” Ukraine has urged its allies to send jets, though the U.K. says it’s not practical to provide the Ukrainian military with British warplanes.

More than 10,000 Ukrainian troops have also been trained at bases in Britain, some on the Challenger 2 tanks that Britain is sending. London’s Telegraph reported that Mr. Zelensky will be visiting some of those troops.

“I am proud that today we will expand that training from soldiers to marines and fighter jet pilots, ensuring Ukraine has a military able to defend its interests well into the future,” Mr. Sunak said. “It also underlines our commitment to not just provide military equipment for the short term, but a long-term pledge to stand shoulder-to-shoulder with Ukraine for years to come.”

The London visit will be Mr. Zelensky’s second known trip abroad since Russia launched its full-scale invasion of Ukraine on February 24. He visited Washington in December.

Mr. Zelensky may be seeking Western pledges of more advanced weapons before potential spring offensives by both Russia and Ukraine.

In Brussels, there were increasing expectations that the Ukrainian leader might also make his first visit to European Union institutions since the war began.

Leaders from the 27-nation bloc will be gathering for a summit at Brussels on Thursday. That would enable Mr. Zelensky to meet with all major leaders of the bloc in one day. The EU’s legislature has also slated a special plenary session in Brussels for Thursday in the hopes that Mr. Zelensky will come following his trip to Britain.

The London visit came as Russian forces blasted areas of eastern Ukraine with more artillery bombardments, Ukrainian officials said Wednesday, in what Kyiv authorities believe is part of a new thrust by the Kremlin’s forces before the invasion anniversary.

Russian forces over the past day launched major shelling attacks on areas near the front line in Ukraine’s northeastern Kharkiv region, killing a 74-year-old woman and wounding a 16-year-old girl in the border town of Vovchansk, the local governor, Oleh Syniehubov, said.

Russian forces in Ukraine are focusing their efforts on “waging a counteroffensive” in the country’s industrial east, with the aim of taking full control of the Donetsk and Luhansk regions that make up the Donbas, the General Staff of the Armed Forces of Ukraine said.

Russian troops launched assaults near Bakhmut and Vuhledar, two mining towns in the Donetsk region that have been among Moscow’s key targets, Ukrainian officials said. Seizing Bakhmut could severely disrupt Ukraine’s military supply routes. It would also open a door for Moscow’s forces to drive toward key Ukrainian strongholds in Donetsk.

Ukrainian authorities say the Kremlin’s goal is to complete full control of the Donbas, an expansive industrial area bordering Russia. That would give President Putin a major battlefield success after months of setbacks and help him rally public opinion behind the war.

Military analysts say that after a Ukrainian counteroffensive that started last summer and recaptured large areas from Russia, the war has been largely static in recent months.

Russia is now also trying to break through Ukrainian lines near the towns of Avdiivka and Marinka in Donetsk, as well as near Kreminna, a front-line town in the Luhansk region which lies along a key Russian supply route, the Ukrainian General Staff said.