NATO boss Mark Rutte and EU chief Ursula von der Leyen on Sunday paid tribute to US Senator Lindsey Graham after his sudden death.

“So sad to learn of the sudden passing of my friend Lindsey Graham,” Rutte posted online.

“He was a powerful advocate for America who believed strongly in the NATO alliance and was actively working to bring an end to Russia’s war against Ukraine.”

European Commission president von der Leyen said Graham was “a determined and fearless leader. He will be deeply missed.”

“Senator Graham fought until the very end to support Ukraine’s fight for freedom and raise the cost of Russia’s war of aggression. He worked tirelessly to strengthen sanctions, in close coordination with the EU,” she wrote.

The prominent Republican senator, a key ally of President Donald Trump, died on Saturday aged 71 following a “brief and sudden illness”, his office said.