Updated

The arrests of seven men suspected of plotting a major extremist attack somewhere in the Netherlands neutralized "the concrete threat" the cell posed, the Dutch counterterror coordinator said Friday.

The men were attempting to obtain AK-47 assault rifles, handguns, bomb vests, grenades and raw materials for bombs and were looking for opportunities to train with such weapons, prosecutors say.

Later Friday, prosecutors said in a statement that "large amounts of raw materials for explosives for bomb vests and 100 kilograms (220 pounds) of fertilizer, possibly for use in a car bomb" were seized during raids on the suspects' homes. Police also seized five handguns during Thursday's raids.

The group allegedly wanted to attack a large event and planned to detonate a car bomb at another location. Investigations into the suspects' possible target are continuing.

The National Coordinator for Counterterrorism and Security said in a statement that the threat level in the Netherlands remains unchanged at four on a scale of five.

"These arrests have removed the concrete threat of a terrorist network," the coordinator said.

"There is no reason to avoid events," the statement added. "But at the same time we remain realistic: We can never guarantee 100 percent security."

The seven suspects, whose ages ranged from 21 to 34, appeared before an investigating judge Friday at a closed-door hearing and their detention was extended until next week. The suspects' identities haven't been released.

About 400 police took part in raids Thursday that led to the arrest of the men. Three of them, including the alleged ring leader, a 34-year-old Iraqi, have previously been convicted of attempting to travel overseas to join extremist networks.

Dutch media reported that one of the suspects had previously been detained but not charged after taking photographs at a military airbase where he was working.

Prime Minister Mark Rutte expressed gratitude to the security services for the raids and said that while an attack had been foiled, the arrests "show how important it is that we remain alert."