MADRID (Reuters) - Spanish police have arrested four people suspected of involvement in a migrant network with connections to Islamic State, the Interior Ministry said on Monday.

Islamic State is believed to have used the network to smuggle militants into Europe via Turkey among migrants fleeing Syria's civil war, the ministry said. These have included militants involved in the November 2015 Paris attacks.

The four are also under investigation for links to two people detained in Austria last year with suspected connections to the Paris attackers.

Two of the detainees are residents of the north-west Spanish region of Galicia while the other two operated in the southern province of Andalusia, the ministry said. It gave no further information.

Since Spain raised its national security threat alert in 2015, authorities have detained about 168 people on suspicion of involvement in Islamist militant activity.

(Reporting by Amanda Calvo; Editing by Paul Day and Gareth Jones)