Spain is marking the 10th anniversary of the Madrid train bombings which ripped apart four packed commuter trains, killing 191 people and leaving about 2,000 wounded.
Tuesday's anniversary comes as security forces continue to grapple with new and emerging threats from al-Qaeda-linked groups, the AFP news agency reported.
The Spanish royal family led by King Juan Carlos, as well as Prime Minister Mariano Rajoy, will join a mass for victims in Madrid's Almudena Cathedral, a solemn ceremony for a nation still wary of jihadists and "lone wolves" lured to their cause.
The shrapnel-filled bombs detonated at 7:40am on March 11, 2004, in packed commuter trains headed to Madrid's main Atocha railway station.
Physical and psychological scars of the deadliest terrorist attack in Spanish history still run deep.
Antonio Gomez, a married 48-year-old bank computer designer with daughters now aged 10 and 15, was in a train at Atocha when a bomb detonated.
He said he was reading a newspaper that protected his face from the flying shards of shattered windows.
"But bits of glass embedded in the face of a little girl beside me," he recalled.
With a fellow passenger, Gomez said he managed to force open a door of the collapsed train, as people trampled over each other to escape onto the platform.
He called his pregnant wife on his cell phone.
"Just after telling her what happened and not to worry because I am all right, that is when the second bomb went off and the mobile was cut off," Gomez told AFP.
"The blast wave caught me and I fell to the platform, and the blow broke my left leg," he said.
"There were mutilated people, people thrown on the ground, people in a very bad state. I was one of the better off. It was Dantesque. I don't like to remember it."
Al-Qaeda's leaders and its affiliates, including north African group, Al-Qaeda in the Islamic Maghreb and armed groups fighting the government of Syrian President Bashar al-Assad, refer frequently in their statements to "Al Andalus", in reference to Spain, he said.
"Clearly Spain forms part of the strategic objectives of global jihad. We are not the only ones but we are in their sights obviously," said Jorge Fernandez Diaz, Spain's Interior Minister.
Since the day of the bombings, 472 suspects linked to armed groups have been arrested in Spain, Fernandez Diaz said.
Some 1,800 Spanish police and counter-terrorist security forces, in addition to the intelligence service, now grapple with the threat of a new attack, the minister said.