Erdogan announced late on Wednesday that he had replaced those three ministers, for the interior, economy, environment and even his European affairs minister, and reshuffled the justice, transport, family, sports and industry portfolios, and one of his four deputy prime ministers' posts.

The reshuffle was decided in a closed-door meeting with President Abdullah Gul, who had said since Tuesday that it was imminent.

There was no indication the characteristically defiant Prime Minister was himself contemplating stepping down, as demanded by anti-government protesters and by the environment minister who resigned, Erdogan Bayraktar.

Yet the corruption scandal is rapidly becoming a major challenge to Erdogan's 11-year grip on power in Turkey, a NATO member and significant emerging economy.

His image was already badly bruised in June when he ordered a heavy-handed crackdown on anti-government protests sparked by plans to raze an Istanbul park.

Another protest took place in Istanbul on Wednesday demanding Erdogan's ouster, but police used tear gas to disperse the estimated 5,000 demonstrators after some skirmishes. Protests were also reported in Ankara and Izmir.

The probe into the corruption, which has seen recent police raids, focus on allegations of numerous offences including accepting and facilitating bribes for construction projects and illegally smuggling gold to Iran.

Erdogan himself has sought to define the corruption scandal as "a conspiracy" plotted by "international powers".

He insists his ruling Justice and Development Party (AKP) party has a clean record and has responded to the investigation by sacking dozens of police chiefs.