Air defences were engaged in Ukraine's capital of Kyiv on Thursday to repel a Russian drone attack, officials said, and Reuters witness reported explosions in the city while British Prime Minister Keir Starmer was visiting.

While air raid sirens during visits by foreign leaders have sounded before, it is rare for air defenses to actually have to fight off attacking drones.

Ukrainian President Volodymyr Zelenskyy warned allies that the defense of his nation is a litmus test for broader Western resolve.