Hungarian anti-terrorist police last week detained four people heading to the capital with explosives in their car, and found a bomb-making laboratory set up for a mass killing, the unit's chief said on Tuesday, declining to rule out a link to Islamist militants.
Security has been tightened for senior officials entitled to "top protection," the Counter Terrorism Centre said in a statement.
The center's director-general, Janos Hajdu, said the suspects had been detained last week as police stepped up investigations that touched on the security of these officials, whom he declined to name.
After the suspects in the car were detained, a subsequent house search revealed a bomb-making laboratory with "explosives and devices that were suitable for killing people to the utmost extent," Hajdu told the state television channel M1.
He said police had also caught two other people with submachine guns, ammunition and silencers in their car, and that it was not clear whether the two groups were connected.
Asked whether the suspects had jihadi links, he said: "Let me reply to that in the next few days."
Hajdu declined to disclose the suspects' identities, nationalities or presumed motives, but added that the case had an international dimension.
Much of Western Europe has been on high alert since Islamist militants killed 130 people in coordinated attacks in Paris on Nov. 13 that were claimed by Islamic State, and Brussels has been in lockdown for several days because of fears that another attack is imminent.
Counter Terrorism Centre officials were not immediately available for further comment.
M1 said two of the suspects had been formally placed under arrest, and a court would decide on the others on Wednesday.
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