The Turkish government fired 350 police officers in Ankara overnight, including heads of major departments, amid a vast corruption scandal that has ensnared key allies of Prime Minister Recep Tayyip Erdogan, local media reported on Tuesday.

The officers were sacked by a government decree published at midnight and included chiefs of the financial crimes, anti-smuggling, cyber crime and organised crime units, the private Dogan News Agency reported.

The move comes as the government is trying to contain the high-level corruption probe that poses the biggest threat to Erdogan's 11-year rule.

It has also exposed the influence of an exiled Muslim scholar on Turkey's halls of power and his byzantine relationship with the government.

The investigation is believed to be linked to simmering tensions between Erdogan's government and followers of influential Muslim scholar Fethullah Gulen, who lives in exile in the United States.

Gulen followers hold key positions in various government branches including the police and judiciary.

Erdogan has denounced the investigation as a foreign-hatched plot to bring down his government and has responded by sacking hundreds of police officials across the country, including the Istanbul police chief, since the probe first burst into the open in mid-December.

Erdogan's critics accuse him of desperately trying to protect his cronies, and the appointment of Selami Altinok, a little-known governor with no background in police work, as Istanbul's new police chief was further seen as an attempt to shut down the investigation.

The crisis erupted on 17 December when police arrested dozens of people including sons of former ministers and the chief executive of Turkey's state-run Halkbank. They are suspected of numerous offences including accepting and facilitating bribes for development projects and securing construction permits for protected areas.

Erdogan has vowed to battle "a state within a state", apparently referring to Gulenists in the state apparatus and said he would not allow parallel structures.

Gulen, who has been living in self-imposed exiled in the US state of Pennsylvania since 1999, has denied any involvement in the controversial inquiry. His followers were key backers of Erdogan's AKP when it came to power in 2002.

The turmoil has rattled Erdogan's government ahead of key local polls in March and plunged the Turkish lira to an all-time low.

The graft probe has also exposed bitter fault lines in Erdogan's traditional power base and prompted calls from both his own party and opposition parties for the resignation of the entire government.

The European Union, which Turkey aspires to join, urged Turkish authorities to address the graft allegations in an "impartial manner".