British Prime Minister Keir Starmer arrived in Ukraine’s capital on Thursday with a pledge to help guarantee the country’s security for a century, days before Donald Trump is sworn in as U.S. president.

The British government says Starmer and Ukrainian President Volodymyr Zelenskyy will sign a “100-Year Partnership” treaty in Kyiv covering areas including defense, science, energy and trade.

Starmer’s unannounced visit is his first trip to Ukraine since he took office in July. He…