BELLINZONA, Switzerland — Three accused eco-terrorists went on trial under heavy security in Switzerland’s highest criminal court yesterday for an alleged plot to blow up an IBM nanotech research center as it was being built near Zurich.

The trial in the Federal Criminal Court for an Italian couple and Swiss man living in Italy opened after a one-hour delay because of the extraordinary security taken by Swiss police, who cordoned off the area with metal barriers.

The three defendants — 35-year-old Costantino Alfonso Ragusa, his 29-year-old wife Silvia Ragusa Guerini and their 26-year-old Swiss friend Luca “Billy” Cristos Bernasconi — had been detained after being arrested last year with explosives.

Swiss authorities have linked the three to an Italian group that also has claimed responsibility for bombings in Greece, Switzerland and Italy. Experts say a loosely linked movement of European anarchists is becoming more violent and coordinated in the wake of the continent’s financial crisis.

Their defense lawyers said the trial should have been held in Italy and claimed that putting them on trial in Switzerland was unfair because Swiss police had used a “staged traffic control” to arrest the defendants.

“This is a violation of the law which prescribes presumption of innocence for anybody,” said lawyer Christian Meier, representing Bernasconi. Marcel Bosonnet, a lawyer for Costantino, agreed.

The three were stopped in traffic in April 2010 near Zurich, about two miles (three kilometres) from what police said was their intended target, the IBM research center at Rueschlikon that opened in May.

The court dismissed the defense objections, saying Zurich police had acted correctly.

The three had left Italy a day earlier, and the police said a search of them and their car turned up explosives hidden in the woman’s clothing and other materials used for bomb-making in a bag they carried. Since their arrests they had been held in separate Swiss prisons.

During their confinement, in March, a letter bomb exploded at an office of the Swiss nuclear power industry in the northern city of Olten, wounding two people. That occurred just hours before another package exploded at a military barracks in Italy, wounding one person, and authorities in Greece defused a mail bomb sent to a maximum security prison where alleged members of an armed anarchist group were on trial.

The Italian bombing was claimed by anarchists, who the Italian police said had also sent letter bombs in December to the embassies of Greece, Chile and Switzerland in Rome as part of a campaign with jailed comrades in Greece.

Swiss authorities say the attacks on the Swiss embassies in Athens and Rome came in retaliation for the arrests of Ragusa, Guerini and Bernasconi.

At the trial Tuesday, a prosecutor, Hans-Joerg Stadler, presented evidence that the police had found explosive gel and several types of fuel that were to be used in the planned IBM attack. A chemist and a specialist in defusing bombs told the court the combination was almost as strong as TNT, and could be deadly, and that anyone can find detailed instructions on the Internet on how to use explosives.

Stadler said the police also found 31 handwritten letters claiming responsibility for the planned attack signed on behalf of “ELF Switzerland, Earth Liberation Front.” The letters, according to police, described the three as revolutionary “eco-anarchists” and said their attack on the IBM center was meant to be “as destructive as possible.”

The Earth Liberation Front, or ELF, is an environmental extremist movement of people or cells that was founded in Britain and spread through Europe in the early 1990s. Since then U.S. authorities also have considered ELF, which is closely associated with the Animal Liberation Front, one of their top domestic terror threats.

Biotechnology is used to create new drugs and conduct research with plants and animals. Nanotechnology involves manipulating and making new materials between 1 and 100 nanometers in size; one nanometer equals one billionth of a meter.

Both are increasingly being used particularly for agriculture, medical and military uses, but there has been much public debate — and criticism from environmental and animal-rights groups — about the implications for the environment.

About 60 protesters gathered outside the courthouse with loudspeakers and banners Tuesday demanding freedom for defendants and opposing biotechnology, nanotechnology and nuclear power. The trial is expected to end Wednesday, with a verdict given Friday.

IBM’s website says Zurich is considered by many as the birthplace of nanotechnology, and its new $90 million research center a place where “scientists will research novel nanoscale structures and devices to advance energy and information technologies.”