WASHINGTON - AFL-CIO President Richard Trumka, head of the largest U.S. labor organization and a key figure in Democratic politics, has died at age 72, representatives for the group said on Thursday.

President Joe Biden told reporters at the White House that Trumka was a close personal friend. Trumka died unexpectedly of a likely heart attack, a source told Reuters.

Trumka, a third-generation coal miner from Nemacolin, Pennsylvania, began working in the mines at age 19, and became president of the AFL-CIO, a federation of 55 unions representing 12.5 million workers, in 2009.

He presided over the AFL-CIO at a time of increasing challenges for the American labor movement. Trumka had pushed U.S. lawmakers to revise trade deals and make it easier for unions to organize new members.

"Working people of America have lost a fierce warrior at a time when we needed him most," said Senate Majority Leader Chuck Schumer, a Democrat. "We have just lost a giant."

Local chapters of the labor group in Philadelphia and Ohio posted condolences on Twitter announcing his death. Many U.S. lawmakers also posted messages of condolences about Trumka.

An official for the labor organization and another major union president speaking on the condition of anonymity also confirmed the death to Reuters. A union spokeswoman did not immediately comment.

"It is with great sadness and a heavy heart that we have learned @AFLCIO President Richard Trumka has passed away. You have been a champion for workers and an incredible pillar in the fight for workers' rights," the Philadelphia unit tweeted.

"We will continue your never-ending fight for social and economic justice for every working person," the Ohio chapter also said on Twitter.