Spain marked the 15th anniversary of the country’s most deadly terror attack on Monday.

A series of explosions in morning commuter trains traveling into Madrid's main Atocha station killed 192 people and injured more than 2,000 others.

The 15th anniversary of the atrocity was marked with a number of commemorative events across the capital.

Surviving victims, relatives and political leaders came together at a remembrance ceremony outside Atocha station.

Red carnations were laid and scores of candles were lit at the site in memory of the tragedy.

A cloud of white balloons was released into the air after a solo saxophonist performed on stage to a somber crowd.

The main political parties came together in a joint act of solidarity for the victims, their families and the public and emergency services who came to their aid.

Spanish Prime Minister Pedro Sanchez, Mayor of Madrid Manuela Carmena and Madrid’s regional President Angel Garrido attended a wreath-laying ceremony at Puerta del Sol.

They observed a moment of silence during the event in the city's main square.

Sanchez described the attack as an act of “barbarism” in a post on Twitter.

“It was the most tragic attack in our history," said the PM.

He said the victims who were “snatched from us” and those who “live each day with the pain of the memory” will never be forgotten.

An act of remembrance for the victims was held at the Forest of the Departed memorial in downtown Retiro Park.

The bombs detonated on four packed commuter trains heading into Atocha during the morning rush hour on March 11, 2004.

A total of 193 people lost their lives as a result of the atrocity: 34 at Atocha station, 63 at Téllez Street, 65 at El Pozo Station, 14 at Santa Eugenia Station and 16 in different hospitals.

The last victim died in 2014 having spent 10 years in a coma.

They were of 17 different nationalities, among them 143 Spaniards.

More than 2,000 other people were injured in the attack, the deadliest in Europe since the 1988 bombing of a Pan Am flight over Lockerbie, Scotland.