Chile has sought help from foreign security agencies in an effort to find those responsible for an explosion that injured 14 people at a subway station in the capital, Santiago.
A number of bomb scares and small blasts have also kept the country on edge in recent days.
Prosecutor Raul Guzman did not say which countries had been contacted, but that “international agencies” had been asked for help to investigate the explosion – the latest in a wave of 29 small bombings or attempted bombings in Santiago this year.
While no-one has claimed responsibility for Monday’s attack in the city’s upmarket Las Condes neighbourhood, police say they are looking at anarchist groups.
President Michelle Bachelet has boosted security at subway stations and elsewhere and has said she will use the country’s tough, dictatorship-era anti-terrorism laws to tackle the case.
Tensions have risen over a spate of bomb scares and two explosions of low-powered devices at supermarkets in the town of Vina del Mar, which appeared to be designed to make noise but cause little damage.
Santiago is one of the safest capitals in Latin America, but residents have been rattled by the bombings, especially after Monday’s blast – the first to cause injuries. Earlier attacks were small explosions at cash machines, churches and subway stations which caused no casualties. Sometimes bombs did not go off.
“Now I’m thinking twice before I take the subway because I am pregnant,” 26-year-old teacher Romina Celle said.
Joanna Magneti, who works at the underground shopping centre where the metro is located, said after Monday’s blast: “I was having lunch when I felt the bang. I saw lots of smoke, people running and shouting, a youngster who was badly injured and a woman with an injured hand.”
Adding to concerns were clashes yesterday on the 41st anniversary of the coup that ousted Marxist president Salvador Allende and began the dictatorship of General Augusto Pinochet.
Seven people were arrested after stones and petrol bombs were thrown at police in Santiago, and a bus was set on fire.
Chileans remain divided over Pinochet’s 17-year rule and violent protests often happen around the coup’s anniversary.
The latest bombing is one of the worst since democracy was restored in 1990.
There have been around 200 bomb attacks in Santiago since 2005, largely by shadowy anarchist groups. Bombs often explode outside banks and other targets, such as police stations, army barracks, and the headquarters of political parties, though with few injuries.
The only person killed in the past decade was Mauricio Morales, a young anarchist who died in 2009 when the device he was carrying exploded prematurely.
Two years later, another anarchist was severely injured when a bomb he was planting at a bank exploded in his hands.
Around 80 different groups have claimed responsibility and prosecutors have struggled to determine if they are dealing with one group that changes its name or many.
One group calls itself The Friends of Gunpowder. Others are named after anarchists from Europe and the US. One named after Leon Czolgosz, an anarchist who assassinated US president William McKinley in 1901, has claimed responsibility for at least five attacks..