MADRID - Close to 80 years ago, Picasso painted Guernica in a Paris attic, a haunting work of art that has become a universal howl against the ravages of war, from 1937 Spain to 2017 Syria.

The canvas mixes stark images of agonizing humans and animals to depict the horror of the bombing of the small Basque town of Guernica on April 26, 1937 during Spain's civil war.

Luis Ortiz Alfau, a 100-year-old Spaniard, was there that day "to pick up the dead and the injured", he said.

"Around 4 pm, three planes started arriving every 15 minutes, they were German and Italian planes," said the former soldier on the Republican side.

"They dropped bombs, then incendiary bombs, and the town started to burn."

To mark the 80th anniversary of one of the most famous paintings in the world, studied by generations of schoolchildren, Madrid's Reina Sofia Museum, where it now hangs, will hold a major exhibition from Tuesday.

"Guernica's importance in the collective unconscious is such that I define it as a spiritual work of art, with a constant vocation of promoting peace," said Bernard Ruiz-Picasso, the artist's grandson.

Rosario Peiro, head of collections at the museum, said Syrians had used images of the painting in their protests. They "were trying to say: 'Enough with this war in Syria'".

At the United Nations last year, French Ambassador Francois Delattre compared the destruction in the Syrian city of Aleppo to Guernica.

"Aleppo is to Syria what Guernica was to the Spanish war, a human tragedy, a black hole destroying all we believe in," he said.

'Screaming out'

The Spanish Civil War kicked off nine months before the attack on Guernica when army generals staged a coup against a fledgling left-wing republic. Led by General Francisco Franco, the nationalist camp had the support of Nazi Germany and fascist Italy.

The attack, which is estimated to have left 150 to 300 dead, was the Nazis' first attempt at terror bombing civilians - a tactic they would go on to use in World War II.

Two days later, Pablo Picasso, who had lived in France since 1904, saw the first photo reports of the tragedy. On May 1, he started his own Guernica.

On a large canvas more than seven meters wide, he painted deformed figures of women and children writhing in a burning city.

A broken sword in hand, a dismembered fighter lies with wide open eyes, an impassive bull, a wounded dove and an agonizing horse nearby.

"It seems the faces are screaming out," said Takahiro Yoshino, a 20-year-old Japanese tourist contemplating the painting for the first time in the Reina Sofia, which saw 3.6 million visitors last year.

Nearby, Sonia Seco Cacaso had taken her kindergarten class to see Guernica.

"When there is a problem, you have to resolve it and not through war," she told them.

Agence France-Presse