Turkey's state-run news agency says 49 people with alleged links to the Islamic State group have been detained for planning "sensational attacks" in the run-up to Sunday's referendum on increasing the powers of the president.

The Anadolu news agency reported Saturday that police conducted simultaneous operations in seven Istanbul districts following a tip. Forty-one foreigners are among the detained. Anadolu says the suspects are also connected to the perpetrators of the New Year's nightclub attack in Istanbul.

IS has called for attacks against the referendum in its Arabic and Turkish publications this month, arguing that voting is opposing God and branding Muslim voters as "disbelievers."

Turkey is holding a referendum on constitutional amendments that would significantly expand the powers of the president.