Former German foreign minister Guido Westerwelle, who shunned NATO's military intervention in Libya in 2011, has died at age 54.

A strong advocate of the "culture of military restraint," Westerwelle died from blood cancer on Friday.

His foundation had announced in mid-2014 that Westerwelle had been diagnosed with acute leukemia. He last appeared in public in November, presenting a book on his battle with blood cancer called "Between Two Lives".

He was the leader of the Free Democratic Party (FDP) from 2001 until 2011 and foreign minister during Chancellor Angela Merkel's second term from 2009 until 2013.

"I'm lost for words. Guido has fought so hard. The grief is great," FDP leader Christian Lindner said in a tweet.

Westerwelle was committed to promoting free markets and small government, with tax cuts at the heart of his party's election programs.

Born in Bad-Honnef, near Bonn in western Germany in 1961, he trained as a lawyer and was elected to the Bundestag lower house of parliament in 1996.

He became chairman of the FDP five years later and was widely credited with broadening the appeal of the party, especially among younger voters.

In the run-up to the 2002 federal election, Westerwelle tried to stir up voters with an American-style campaign, traveling around Germany in a bus dubbed the "Guidomobil", but fell well short of his declared target of winning 18 percent of the vote and remained in opposition.

Seven years later, however, the FDP won nearly 15 percent of the vote, its best-ever election result.

Westerwelle became foreign minister and vice-chancellor under Merkel.

In March 2011, he came under fire for siding with China and Russia and abstaining in a vote in the United Nations Security Council authorizing a no-fly zone over Libya, a mission that later led to the ouster of long-time dictator Muammar Gaddafi.

The move looks like the right decision with hindsight given the turmoil that has swept Libya since Gaddafi's fall. But at the time, Westerwelle was criticized for ignoring decades of German policy in breaking with western allies like the United States, Britain and France.

Later that year, following heavy losses in regional elections, Westerwelle was forced to give up the leadership of the FDP. Two years later, the party failed for the first time in the post-war era to make it into the German parliament.