LONDON — The police in Finland arrested Iraqi twin brothers on Tuesday suspected of being members of the Islamic State and of shooting 11 unarmed prisoners in Iraq in June 2014, Finnish news reports said Thursday.

Finland’s National Bureau of Investigation said on Thursday that the men had arrived in Finland in September and were arrested following an investigation. News reports said they did not resist arrest.

Finnish law enforcement officials did not specify whether the men had arrived as part of the influx of migrants to Europe from the Middle East and beyond. But the Finnish national broadcaster, Yle, reported that the men, who are 23, were asylum seekers, and the arrests intensified concerns that terrorists were slipping into the stream of refugees in an effort to avoid detection by security forces.

Yle, citing the National Bureau of Investigation’s chief inspector, Jari Raty, said the men were suspected of killing 11 people during a massacre by the Islamic State of as many as 1,700 unarmed Iraqi soldiers in June 2014 at Camp Speicher near Tikrit, northwest of Baghdad.