Istanbul: President Tayyip Erdogan tightened his grip on Turkey on Saturday, ordering the closure of thousands of private schools, charities and other institutions in his first decree since imposing a state of emergency after the failed military coup.

Turkish authorities also detained a nephew of Fethullah Gulen, the US-based Muslim cleric accused by Ankara of orchestrating the July 15 coup attempt, the Anadolu state news agency reported.

A restructuring of Turkey's once untouchable military also drew closer, with a planned meeting between Erdogan and the already purged top brass brought forward by several days.

The schools and other institutions are suspected by Turkish authorities of having links to Gulen, who has many followers in Turkey.

Gulen denies any involvement in the coup attempt in which at least 246 people were killed.

His nephew, Muhammed Sait Gulen, was detained in the northeastern city of Erzurum and will be brought to the capital Ankara for questioning, Anadolu reported.

Critics of Erdogan fear he is using the abortive coup to wage an indiscriminate crackdown on dissent. The foundations targeted include, for example, the Association of Judges and Prosecutors, a secular group that criticised a recent judicial law drafted by Erdogan's Islamist-rooted AK Party.

Turkey does not plan to extend emergency rule beyond a period of three months following the failed coup, but will do so if necessary, Prime Minister Binali Yildirim said.

"Our goal is that it shouldn't be extended, but if the need arises it may of course be extended," he said in an interview with the ATV television station.

In his decree, published by the Anadolu state news agency, Erdogan also extended to a maximum of 30 days from four days the period in which some suspects can be detained.

Erdogan, a popular but polarising figure who has dominated Turkish politics since 2003, declared the state of emergency late on Wednesday.

Turkish authorities have already launched a series of mass purges of the armed forces, police, judiciary and education system, targeting followers of Gulen, who operates an extensive network of schools and charitable foundations.

The first decree signed by Erdogan authorises the closure of 1043 private schools, 1229 charities and foundations, 19 trade unions, 15 universities and 35 medical institutions over suspected links to the Gulen movement, the Anadolu agency said.

Parliament must still approve the decree but requires only a simply majority, which the government has.

Reuters