Dozens of police officers have been detained in Turkey as part of an investigation into alleged spying and illegally wire-tapping Prime Minister Tayyip Erdogan and his inner circle.

At least 33 police officers were said to have been detained in 14 provinces across the country.

Last month dozens more were remanded in custody on pending charges that they formed a criminal organisation and bugged phones following a first wave of arrests that started on 22 July.

The arrests come just days before a presidential election on 10 August in which Mr Erdogan hopes to become Turkey's first directly elected president.

Presidents were previously voted for by parliament.

The investigation is widely seen as targeting a "parallel structure" within the state, a term coined by Mr Erdogan to describe members of the police, judiciary and other institutions loyal to US-based Islamic cleric Fethullah Gulen.

Mr Erdogan has accused Mr Gulen of being behind a plot to oust him.

Previously Mr Erdogan declared a "witch hunt" against Mr Gulen's followers, whom he claims are a potential threat to national security.