BERLIN — Three Syrian men who entered Germany with a wave of migrants were arrested Thursday on suspicion of planning an Islamic State attack on the city of Düsseldorf, potentially thwarting a deadly operation that appeared eerily reminiscent of the recent assaults on Brussels and Paris.

The suspected plot, German authorities said, involved suicide bombers, firearms, and explosives — a lethal combination that has become the hallmark of a new spate of Islamist terror in Europe. A fourth man, who prosecutors said had informed French officials about the alleged plot, was being held in France.

The arrests highlighted the significant threat to Europe from Islamic State militants posing as migrants. Officials said all four Syrians entered the continent from the Middle East using the same passages by land and sea — Greece via Turkey and then through the Balkans — used by hundreds of thousands of asylum seekers last year. After the attacks in Brussels and Paris, Islamic State officials have claimed that more sleeper cells were incubating in Europe. Thursday’s arrests suggested such threats were not idle.

The German chief prosecutor’s office said in a statement that there were no immediate indications that the men had started taking concrete steps to carry out the plot. But the authorities moved in on Thursday — arresting the men in three German states — after details of the alleged plot were provided by the suspect in France, who first approached authorities in Paris in February.

The plot, officials said, was supposed to involve two suicide bombers. Other assailants “were supposed to kill as many bystanders as possible with guns and other explosive devices,’’ prosecutors said.

Two of the men were suspected of being active members of the Islamic State, while a third was believed to have at least supported the group. Investigators also suspect that one of the two Islamic State adherents had links to the radical Islamist group Jabhat al-Nusra, the Syrian affiliate of Al Qaeda.

Revelations that the suspects had entered Germany as migrants quickly fueled the debate here over the security threat presented by a massive pool of poorly screened asylum seekers. Hundreds of thousands of would-be refugees entered Germany last year after receiving only cursory vetting in near-bankrupt Greece. Over the past six months, more than three dozen suspected militants impersonating migrants have been arrested or died while planning or carrying out terrorism. They include at least seven directly tied to the attacks in Paris and Brussels.

Although a tenuous deal between the European Union and Turkey has largely blocked new migrants from entering Europe via Greece, more than a million have already arrived. Only a small fraction, officials say, present genuine security threats. But on Thursday, critics took aim at a haphazard migrant policy that was riddled with risk.

A series of coordinated terrorist attacks killed 130 people in Paris in November. The Islamic State claimed responsibility for the massacre, in which at least eight assailants armed with explosives and automatic weapons gunned down people at random at several locations in the French capital.

The Islamic State also claimed a series of attacks in Belgium in March targeting the Brussels airport and a metro station. Three suicide bombings killed 32 people and injured more than 300 as authorities closed in on suspects wanted in the Paris attacks.

Germany’s chief federal prosecutor identified the three arrested Syrians only as 27-year-old Hamza C., 25-year-old Mahood B., and 31-year-old Abd Arahman A.K. It is customary in Germany to withhold the last names of arrested suspects.

The men were arrested in the states of North Rhine-Westphalia, Brandenburg, and Baden-Württemberg. Their apartments were being searched, officials said.