Turkish Prime Minister Tayyip Erdogan's government purged hundreds of police officers last night according to media reports.

The move came as part of a crackdown on a rival he accuses of trying to usurp state power by tarring him with a specious corruption investigation.

Some of the officers, who included members of the financial and organised crime, smuggling and anti-terrorism units, were moved to traffic duties, according to the reports.

Ankara police, the chief focus of the action, declined to comment.

Despite the dismissals, among them senior commanders, police and prosecutors continued arrests, which today targeted the state railway company and a western port.

Mr Erdogan, facing the biggest challenge of an 11-year rule that has seen the army banished from politics, the economy booming and Turkey pressing its role in the Middle East, portrays the raids and arrests as a "dirty plot" by an Islamic cleric.

The cleric backs no political party but exercises broad, if covert, influence in the police and judiciary.

The corruption scandal is shaking investor confidence in Turkey at a time when the lira currency is languishing at record lows, inflation is rising and growth slowing.

As much as its Islamist-rooted ideology, AK Party's support has relied on its avowed commitment to fight corruption and its economic record.             

Uncertainty caused by the scandal could hit economic growth in the short term, Finance Minister Mehmet Simsek said, while ratings agency Fitch warned today that a prolonged crisis could weaken Turkey's creditworthiness.

Details of the corruption allegations have not been made public, but are believed to relate to construction and real estate projects and Turkey's gold trade with Iran, according to Turkish newspaper reports citing prosecutors' documents.

Prominent business people, the sons of three cabinet ministers and state officials are among those to have been detained for questioning.

Among the dozens questioned, most have been released.

A remaining 24, including two of the ministers' sons, have been remanded in custody, according to local media.

The government has hit back by sacking or reassigning hundreds of police across the country since the crisis broke, with a day of raids and arrests on 17 December.