MADRID, Spain (CNN) -- Spain commemorated victims of the March 11, 2004 Madrid train bombings with somber ceremonies on Tuesday at three stations in the capital where 191 people died in the Islamic terrorist attacks.
A bouquet of flowers for a victim of the 2004 bombings is attached to railings near Atocha station.
King Juan Carlos and Prime Minister Jose Luis Rodriguez Zapatero attended the main ceremony at Atocha station, where most of the casualties came when bombs exploded on one train inside the station and a second on the tracks just outside.
Some of the survivors of the attack, which left 1,800 people wounded, gathered with the king and prime minister at the train bombing monument -- a circular glass structure in front of the station that was inaugurated on the third anniversary of the attacks.
There were no speeches, just the placement of a floral wreath and the performance of "Da pacen domine," a song for peace, by an orchestral and choir ensemble.
Other smaller memorials were held at the Santa Eugenia and Pozo stations down the line from Atocha, where the other two trains were torn apart by explosions four years ago.
"This year it was especially delicate to reach the anniversary," Pilar Manjon, who lost a son in the bombings and is president of the March 11 Victims Association, told Spanish radio network SER. "Everything has been stirred up again. There were elections again."
Zapatero won an upset victory in 2004 three days after the bombings, and was re-elected last Sunday.
A Spanish court last October convicted 21 people in connection with the attacks. Seventeen of those were Islamic terrorists and four were Spaniards who were sentenced for supplying explosives stolen from a Spanish mining operation that ended up being used in the attacks. Seven people were acquitted.
Various appeals to that sentence are still pending before Spain's Supreme Court, which is expected to rule on the cases later this year.
A few other suspects thought to be linked to the bombings could yet face trial, including two in Morocco and another in Spain.
Authorities say Spain remains under constant threat from Islamic terrorism. Al Qaeda reports regularly mention Spain -- among other countries -- as a target, and more than 300 suspected Islamic extremists have been arrested in the country since the bombings.
Besides the train bombing trial, a separate trial concluded last month with the convictions of 20 men, mainly Algerians and Moroccans, for Islamic terrorist activity in Spain.
In another case, a judge held in prison for investigation 10 men, mainly Pakistanis, who were arrested last January in Barcelona on suspicion of planning al-Qaeda style attacks in Spain, Germany, France, Britain and Portugal. E-mail to a friend