Turkey’s prime minister has warned that the crackdown following a failed coup was not over, as authorities issued arrest warrants for dozens of former newspaper staff.

More than 15,000 people have been detained for suspected links to the coup and at least 8,000 remain in custody, according to the interior ministry.

Tens of thousands more have been purged from state institutions and the state-run Anadolu news agency said that close to 1,700 officers have been formally discharged from the military following the country’s failed coup. The government has shut down dozens of media organisations, including 45 newspapers and 16 television stations.

Ankara said that Fethullah Gülen, a US-based Muslim cleric, was behind the failed uprising by a faction within the military that led to some 290 deaths on 15 July.

Prime minister Binali Yildirim said: “The investigation is continuing – there are people who are being searched for. There could be new apprehensions, arrests and detentions. The process is not completed yet.”

Energy minister Berat Albayrak, who is the son-in-law of president Recep Tayyip Erdoğan, said Turkish authorities had been planning a major purge of the military and other institutions to remove Gülen-linked elements before the coup attempt. His comments suggested that elements of the military launched the coup attempt because they knew they were about to be purged.

“They were going to take really important steps to remove Gülenist officers and generals from the armed forces. We were already working on this,” said Albayrak, who was with Erdoğan on the coup night.

A large-scale shake-up of the Turkish armed forces is expected to be announced when the country’s supreme military council meets on Thursday.

More than 10,000 soldiers and around half of the 358 generals have been detained, leaving gaping holes in the command structure to be filled.

The Turkish government has also issued arrest warrants for 47 former staff of the Zaman newspaper, which supported Gülen and is suspected of links to the cleric. One official said the swoop covered “executives and some staff, including columnists”, describing Zaman as the “flagship media organisation” of the Gülen-led movement.

In March, Zaman and its English-language sister newspaper Today’s Zaman were taken over by state-appointed administrators and it has since taken a strongly pro-government line. Several former staff are believed to have since left Turkey.

The official said the arrest warrants were not related to what individual columnists had previously said or written. However, “prominent employees of Zaman are likely to have intimate knowledge of the Gülen network and as such could benefit the investigation”, he added.

Earlier this week Turkey issued another 42 arrest warrants for journalists – 16 of whom have been detained, according to Anadolu.