Prime Minister Andy Burnham of Britain arrived in Kyiv, the Ukrainian capital, on Monday along with other European leaders for the country’s Independence Day, in his first foreign trip since taking office.

Mr. Burnham’s visit comes as Russia has sharpened verbal attacks against Britain’s longstanding assistance to Ukraine, warning of consequences if the aid and support continue.

In a statement on Monday following the prime minister’s arrival, Dmitri S. Peskov, the Kremlin spokesman, accused Britain of stoking tensions.

“Britain is taking part in the war — and it is taking part on the side of the Kyiv regime,” he told Russian reporters in a televised briefing on Monday. “Britain has been hellbent on pouring oil on a fire and plotting to prevent any kind of peace process.”

Along with other European countries, Britain has long pushed for a cease-fire in a war that began when Russia invaded Ukraine in 2022. But those efforts have faltered as the United States seized control of the peace process in the last year.

Mr. Burnham appeared to stand firm against the aggressive Russian comments on Monday as British officials announced that he would present President Volodymyr Zelensky of Ukraine with technical plans for a long-range missile.

“Despite Russia’s outrageous threats to my country we will continue our support for you,” Mr. Burnham said in a speech from Sofiivska Square in Kyiv. “This is the moment to keep up the pressure on Russia, to stop their ability to fund this illegal war.”

The missile, jointly built with France, is known as the Storm Shadow in Britain. Officials said that allowing the classified plans to be provided to Kyiv would allow Ukraine and France to build the French version, known as SCALP, on assembly lines inside Ukraine.

Mr. Burnham arrived in Kyiv by train on Monday morning after traveling overnight. Mr. Burnham met with Mr. Zelensky and will chair an in-person and virtual meeting of the “coalition of the willing,” a group of leaders who have pledged support for Ukraine in the war against Russia.

Katarina Mathernova, the European Union’s ambassador to Ukraine, told reporters on Sunday night as she traveled for the coalition meeting that the mood in Ukraine had “darkened” this summer amid targeted Russian attacks on civilians.

She also noted that the war seemed to be moving into a new phase in which both sides try to inflict serious economic damage on the other. Russia is choking off Ukraine’s grain exports through the Black Sea, and Ukraine is targeting economic actors, like Wildberries, a company that is Russia’s equivalent to Amazon.

Jeanna Smialek contributed reporting from Kyiv, Ukraine.