The sources did not know the cause of his death but said he had been suffering from illness.
Although he lived in exile for decades, mostly in France, Carrillo was a central figure in Spanish politics during much of the tumultuous 20th Century and a player in the difficult transition to democracy in the late 1970s after dictator Francisco Franco died.
Carrillo put his longevity down to continued active participation in Spanish political life, writing essays and making contributions to public seminars and a weekly nationwide radio debate well into his 90s.
"I am a politician with a sense of reality," he told Reuters in an interview, explaining his career.
"If you can say anything good about me, it's that I have lived many years and actively participated in many episodes of Spain's history," he said, presenting a documentary in 2009.
An image firmly embedded in the nation's memory is that of Carrillo and Adolfo Suarez, another of modern Spain's founders, refusing to take cover when Civil Guards opened fire in the Spanish parliament in 1981 as part of a thwarted coup.
The son of a union organiser, Carrillo's activism began in 1931, when, at the age of 15, he began reporting for the Socialist Party newspaper and joined crowds to cheer King Alfonso XIII fleeing to exile and the declaration of Spain's Second Republic.
In 1936 he joined the army to defend the Republic from a military revolt which turned into a bloody civil war lasting almost three years and ended up installing Franco as dictator.
Carrillo, by now a Communist, was named a public order official in a defence committee set up in Madrid in November that year just as rebel troops were approaching the capital and the Republican government had fled to safety in Valencia.
After Franco's forces won in 1939 with the help of Nazi Germany and Fascist Italy, Carrillo went into exile, from where he helped organise resistance to the dictatorship.
In 1960 he became general secretary of the Spanish Communist Party (PCE), and began to draw criticism from the Franco regime for his alleged role in the 1936 massacre of several thousand supporters of the military revolt, for which far-right Spaniards blame Carrillo to this day.
The supporters were evacuated from a city jail to Paracuellos, on the outskirts of Madrid, to prevent them from joining Franco's forces which came close to taking the capital, but were then killed en masse rather than incarcerated.
Carrillo always protested his innocence, saying he had little influence as a young and minor official and had no idea what was happening in a chaotic and lawless city under siege, whose people were enraged by bombings and atrocities.
British historian and Civil War specialist Paul Preston spent a year researching Paracuellos for his 2011 book "The Spanish Holocaust" and concluded that while the massacre itself was most likely the work of anarchists and soldiers assessed by Soviet military advisers, Carrillo did help organise the evacuation.
"Carrillo was an important part in the second phase (organisation), and his many statements that he knew nothing and it was all the anarchists' fault are not truthful," he said.
"This does not mean that Paracuellos is his work alone. He was one, and a very important one of many who did this terrible collective deed."
In all, Preston estimates 50,000 Spanish civilians were killed in the Republican rearguard, and another 150,000 behind Franco's lines.
Carrillo had to wait until after Franco's death in 1975 to return to Spain. In 1977 he became a member of parliament in the first elections held in Spain since 1936, but the PCE did poorly and he was expelled from the party in 1982.
Source: Reuters