WARSAW, Poland — Polish authorities have arrested a man who was planning to detonate a four-ton car bomb in front of the parliament building in Warsaw while the president, prime minister, government ministers, and lawmakers were inside.

Prosecutors said Tuesday that they arrested the suspect in Krakow on Nov. 9. They say he is a 45-year-old Polish researcher employed at the University of Agriculture in Krakow who had access to chemistry laboratories. He was in illegal possession of explosive materials, munitions, and guns.

They say the suspect, an expert on explosives, was motivated by nationalistic, xenophobic, and anti-Semitic ideas, but that he does not formally belong to any political group. He is refusing to be submitted to psychiatric testing, they added.

The suspect, who was not identified by name, was building bombs himself and also had detonators, said prosecutor Mariusz Krason.

A secretary at the university said the suspect was a chemist who taught courses, but would give no other details. She spoke on condition of anonymity because she is not authorized to divulge information.

Authorities said the man intended to put four tons of explosives in a car and detonate them outside the parliament building in the heart of the capital while President Bronislaw Komorowski, Prime Minister Donald Tusk, and Cabinet ministers were inside, along with the members of the 460-seat lower chamber.

"The threat of an attack was real," said Artur Wrona, a prosecutor who was among several officials who gave the details of the thwarted terror attack at a news conference in Warsaw.

Krason said the man has confessed in part to the suspicions against him, including planning an assassination of the state leaders. If he is convicted he could face up to five years in prison.

Two others working with him were also arrested for the illegal possession of weapons and two more have been questioned.

The investigation and arrests are being led by the Internal Security Agency. The group published film footage of test explosions in a rural area made by the suspect and found among his possessions.

Both the president and the prime minister were informed of the assassination plan and the investigation before the news was released to the public, said Joanna Trzaska-Wieczorek, a spokeswoman for the president.