United States President Joe Biden is in the United Kingdom ahead of a NATO summit aimed at showing solidarity with Ukraine.

The US president will meet Prime Minister Rishi Sunak to discuss the upcoming NATO summit in the Lithuanian capital on Tuesday and Wednesday.

“The UK is Europe’s leading NATO ally; we are the United States’ most important trade, defense, and diplomatic partner; and we are at the forefront of providing Ukraine with the support they need to succeed on the battlefield,” he added.

The White House said Biden will also meet Britain’s King Charles for the first time since his May coronation to hold talks focusing on climate change and the environment.

“As we face new and unprecedented challenges to our physical and economic security, our alliances are more important than ever,” said Sunak.

In a phone call with Turkish President Recep Tayyip Erdogan on Sunday, Biden “conveyed his desire to welcome Sweden into NATO as soon as possible,” the White House said.

The two leaders “expressed their shared commitment to continue supporting Ukraine,” the statement added.