At least 20 people were detained by Turkish authorities in Istanbul and the capital city of Ankara on Tuesday on charges of being involved in illegal wiretapping of Turkish President Recep Tayyip Erdogan’s phone lines in 2013, according to local media reports. The recordings, made public in February last year, allegedly featured Erdogan, who then served as prime minister, and his son, discussing ways to hide over $20 million in cash following raids in government offices.

Arrest warrants were also issued for another 28 people, including 22 from Turkey’s telecommunications directorate and six from the country's Scientific and Technological Research Council, according to local media reports.

The recent arrests come just days after dozens of Turkish police officers were arrested on charges of bugging Erdogan’s phone lines. Hundreds of other police officials were also arrested on similar charges last year, although most of them were later released.

Erdogan won the country’s first direct presidential election in August last year after his stint as the country’s prime minister from 2003 to 2014. He handed over his duties to erstwhile foreign minister Ahmet Davutoglu.

After the recordings were leaked online last year, Erdogan denied their authenticity, reportedly dismissing them as a “vile montage.” Since then, he has repeatedly accused his former ally Fethullah Gulen, a Turkish cleric, of being behind the illegal wiretapping and attempting to undermine the government through a network of loyalists in government institutions. Following his election as president last year, Erdogan has launched a countrywide crackdown on Gulen’s supporters and their “parallel structure” within the security forces.

However, Gulen, who has been living in the U.S. in exile since 1999, has consistently denied Erdogan's claims and has accused the president of trying to evade an inquiry into the corruption allegations leveled against him.

Hurriyet Daily News, a Turkish newspaper, reported on Tuesday that the government had also issued orders to replace police chiefs in several provinces. It wasn’t immediately clear why they were being replaced and if the move was related to Erdogan’s operations against the so-called “Gulenists.”