United States Senator and staunch President Donald Trump ally Lindsey Graham has died, shortly after returning from a visit to Ukraine. 

Mr Graham’s office confirmed the incident in a statement on Sunday morning, stating that the lawmaker died on Saturday night after what it described as a sudden and brief illness.

“On the evening of Saturday, July 11, U.S. Senator Lindsey Graham passed away from a brief and sudden illness. Senator Graham’s family appreciates prayers at this time and asks for privacy during this incredibly difficult period,” the office said.

He was 71.

The nature of the illness remains unknown as of press time, but NBC News reported that emergency personnel responded to a call for “cardiac arrest” at Mr Graham’s home on Saturday night. 

Photos obtained by the media outlet also captured paramedics carrying a person on a stretcher from Mr Graham’s home to an awaiting ambulance while police cars and fire trucks were observed at the scene.

One of Mr Graham’s staff reportedly stated that there was no evidence that he was sick before his death and was scheduled to appear on a programme on NBC News on Sunday. 

Mr Trump has since paid his tribute to Mr Graham, calling him one of the greatest individuals he has ever met. 

“Senator Lindsey Graham, one of the greatest people and Senators I have ever known, is dead! He was always working and was a true American Patriot. Lindsey will be greatly missed!!! Details and arrangements to follow. So sad!” the American leader stated. 

Also, Senate Majority Leader John Thune paid tribute to a “strong advocate for the United States and a strong ally to freedom-loving countries across the globe.”

Ukrainian President Volodymyr Zelenskyy, whom the deceased recently met on Friday, posted, “Lindsey was a true defender of freedom and of the values that make our world safer. We were in constant dialogue, which I will miss.”