Eight men and a woman thought to hold Turkish citizenship were being detained after morning raids at three different addresses in central Athens.

Earlier, police officials told Reuters the individuals were being quizzed for alleged links to the leftist militant DHKP/C, an outlawed group blamed for a string of attacks and suicide bombings in Turkey since 1990.

The police found materials available commercially and which could potentially be used in making explosives were found, they said in a statement. They also retrieved digital material and travel documents.

Witnesses saw police experts in hazmat suits and holding suitcases entering one address in Athens. Tests on an unknown substance found in jars were expected to be concluded within the day.

Turkey’s Erdogan is widely expected to visit Greece in December, although his visit has not been officially announced. It would be the first visit by a Turkish president in more than 50 years.

Another official told the semi-official Athens News Agency that the case was unconnected to domestic terror groups or militant Islamists, and described those questioned as being of Turkish origin.

DHKP/C, known also as the Revolutionary People’s Liberation Party/Front, is considered a terrorist group by the European Union, Turkey and the United States.