President Joe Biden led a chorus of political tributes to Dole and his 35-year career in Congress, paying respect to "an American statesman like few in our history."

"A war hero and among the greatest of the Greatest Generation. And to me, he was also a friend whom I could look to for trusted guidance, or a humorous line at just the right moment to settle frayed nerves. I will miss my friend," Biden said in his statement.

A conservative Republican who campaigned for reining in government, Dole also had a pragmatic streak and sponsored bipartisan legislation during his tenure at the US Capitol, where House Speaker Nancy Pelosi ordered the flags to fly at half-staff in his honor.

"It is with heavy hearts we announce that Senator Robert Joseph Dole died early this morning in his sleep," the Elizabeth Dole Foundation tweeted, announcing his passing.

"At his death, at age 98, he had served the United States of America faithfully for 79 years."

No details were initially provided, but the long-time senator had disclosed in February that he was being treated for stage four lung cancer.

Republican Senate minority leader Mitch McConnell issued a statement honoring his political and military service and saying he joined "the nation in mourning Bob Dole, our good friend and a bona fide American hero."

"Whatever their politics, anyone who saw Bob Dole in action had to admire his character and his profound patriotism."

Dole, born in 1923 in Kansas, was elected to the US Senate in 1968 and was re-elected in 1974, 1980, 1986 and 1992, serving both as Senate majority and minority leader over the years.

In 1976, Dole was tapped by Gerald Ford to be his vice presidential candidate but the Republican ticket lost to Democrats Jimmy Carter and Walter Mondale.

Twenty years later, Dole lost the White House race to Democrat Bill Clinton.

'Kansas war hero'

"When I think of the greatest generation, I think of Senator Bob Dole -- a man who dedicated his life to serving our country. Rest In Peace, my friend," tweeted Senator Mitt Romney, also a former Republican presidential candidate.

Mike Pompeo, who served as secretary of state under former president Donald Trump, described Dole as "a Kansas war hero who believed in America's exceptionalism with his whole heart."

"He devoted his life to serving Kansas & America-in and out of uniform. Our family's hearts are broken," he tweeted.

Tributes also came from the other side of the aisle, with Democratic Senator Bernie Sanders sending his condolences.

"Bob Dole served his country with courage on the battlefield, and with dignity in the Senate."

Dole has long been praised for his military service. He enlisted as an officer in the US Army and in April 1945 was badly wounded in the back and right arm by machine gun fire during fighting against German troops in Italy.

He was hospitalized for more than three years, and the wounds left him with a shriveled right arm.

Self-conscious about the injury, Dole would frequently hold a pen in his right hand to keep people from shaking it.

Social media tributes recalled how he insisted on standing, held up by an aide, to salute the casket of former president George H.W. Bush, who also served in World War II, at his funeral in 2018.

Dole is survived by his daughter Robin, and his second wife, Elizabeth Dole, who herself had a distinguished political career, serving as Secretary of Transportation, Secretary of Labor, and Senator from North Carolina.