"Lindsey basically worked himself to death," US Senator Tommy Tuberville said of Graham's commitment to work. He rarely took vacations and was constantly traveling for work.

U.S. Senator Lindsey Graham died Saturday after a brief and unexpected illness, his office said in statement posted on social media.

Graham had just returned from Kyiv, Ukraine, where he met with Ukrainian President Volodymyr Zelenskyy.

Republican hawk and Iran critic was frequent visitor to Middle East and respected among Gulf leaders

Mr Graham, 71, a veteran senator, is notorious for often urging the US to go to war, especially wars that favour Israel.

Republican lawmaker was vocal supporter of war against Iran

The South Carolina Republican was running for reelection to his fifth term in the Senate, having begun his tenure in 2003.