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

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

Since Russia’s full-scale invasion, the UK gained a reputation for being one of the biggest advocates for aggressive support for Ukraine. But under Prime Minister Keir Starmer’s tenure, President Volodymyr Zelenskiy’s administration and its supporters have grown increasingly concerned about Britain’s more cautious approach.

UK Prime Minister Keir Starmer arrives in Ukraine for security talks with Zelenskyy days before Trump takes office