Dutch investigators revealed on Friday they found a substantial quantity of raw materials for explosives at the homes of seven suspects arrested a day earlier on terror-related charges.

Officers also found "100 kilograms [220 pounds] of fertilizer, possibly for use in a car bomb," prosecutors said.

The men were reportedly planning to carry out a large-scale attack on an event with the aim of causing multiple casualties. The arrests followed a months-long investigation into a terror network.

The suspects, who were not named, made a brief appearance in Rotterdam District Court on Friday. The case was adjourned until next week. The seven men, who range from 21 to 34 years of age, have been remanded under maximum security conditions in the meantime.

Attacked thwarted 

Dutch police said on Thursday they had foiled a major terrorist attack with the arrest of the seven suspected extremists in multiple raids across the country.

"Police arrested seven men on Thursday ... suspected of being at a very advanced stage of preparation for a major terrorist attack in the Netherlands," the public prosecutor's office said in a statement, adding one of the suspects had wanted to kill "many victims."

The suspects were planning to attack a large event with hand grenades, automatic weapons and explosives belts, according to prosecutors.

Police have not yet identified the target of the planned attack, which the prosecutor's office said would have included a separate car bombing.

The arrests capped a months-long investigation that was launched following intelligence that a man of Iraqi descent, the lead suspect, was targeting "a large event in the Netherlands where there would be a lot of victims."

The suspects came from Arnhem, the port city of Rotterdam and villages close to those two cities.

"One of the men from Arnhem wanted to commit an attack with a group at a major event in the Netherlands and kill many victims, according to the Dutch Intelligence Service," the prosecutor's office said.

Prior 'Islamic State' convictions

The 34-year-old man and two of the other suspects were previously convicted of traveling abroad to fight for "Islamic State" militants.

Prosecutors said that the investigation gathered pace this month because of the suspects' "advanced preparations," adding that they were in "search of AK47s, handguns, hand grenades, explosive vests and raw materials for several (car) bombs."

"In a sense it is serious, but luckily it's also good news - a terrorist cell that was plotting an attack has been taken down," Minister for Justice and Security Ferd Grapperhaus told Dutch national broadcaster NOS. "They weren't so far that it was a danger to society, in the sense that it was nearly too late. But they were quite far in their preparations."

Dutch Prime Minister Mark Rutte told journalists on Friday "a drama has been prevented in our country," adding that the chances of a terror attack in the Netherlands "remained a reality."

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kw, ap/kms (AP, Reuters, AFP)