Argentines have been marking the anniversary of the 1994 bombing of a Jewish centre in Buenos Aires that left 85 people dead and about 300 injured.
Argentina's Jewish community has long called for answers to the crime
Thousands of mourners gathered to honour the dead and called once again for investigations to be stepped up and those responsible brought to justice.
Nobody has ever been convicted, but the current government has said it is determined to secure justice.
A prosecutor last year blamed Hezbollah for the blast, which the group denied.
A siren sounded at the precise time the bomb exploded at 0953 (1253 GMT).
People lit candles, laid roses and held aloft photographs of the victims as the names of the 85 dead were read out.
The blast on 18 July 1994 reduced the seven-storey Jewish-Argentine Mutual Association (AMIA) community centre in Buenos Aires to rubble.
The scale of death and destruction left Argentina's 200,000-strong Jewish community, Latin America's largest, in shock.
The anniversary has been declared a day of national mourning
"We were looking for justice but we found impunity," read a large banner at Tuesday's ceremony.
Luis Czyczewsky, whose daughter died in the blast, called for more to be done - not only for the crime to be solved but for Argentina to take a stronger stance against terrorism.
"Today we are left with a sense of impotence, with our anger," he told the crowd.
"Once again, impunity is winning the battle."
Over the years, the case has been marked by rumours of cover-ups and accusations of incompetence but little in the way of hard evidence.
Minor figures, including a policeman who sold the van used in the attack have been named, but no-one has been convicted.
Many accused previous governments of doing too little to find the perpetrators.
The current administration of President Nestor Kirchner has expressed a firm desire to produce results but so far there has been little obvious progress, says the BBC's South America correspondent Daniel Schweimler.
Mr Kirchner's cabinet chief, Alberto Fernandez, said that the courts would do all they could to find the attackers.
Members of the US-based World Jewish Congress (WJC) were to meet the president after the commemorations to add their voices to calls for the authorities to do more.
Local Jewish groups have long said the bombing bore the hallmarks of Iranian-backed Islamic militants.
Iran has repeatedly and vehemently denied any involvement in the attack.
Last November, an Argentine prosecutor said a member of the Islamic militant group, Hezbollah, was behind the attack and had been identified in a joint effort by Argentine intelligence and the FBI.
But Hezbollah said that the man, Ibrahim Hussein Berro, had died in southern Lebanon while fighting Israel.
The 1992 bombing of the Israeli embassy in Buenos Aires, which killed 29 people, also remains unsolved.