Turkish Prime Minister Recep Tayyip Erdogan has replaced nearly half of his cabinet in a reshuffle prompted by a spiralling corruption scandal.

Erdogan announced on television late on Wednesday that he had replaced three resigning ministers and his EU affairs minister, while reshuffling 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.

Erdogan removed Egemen Bagis, the EU affairs minister, from his post. He was excluded from the new line-up and replaced by lawmaker Mevlut Cavusoglu. Bagis was accused of being involved in the corruption scandal but has never been detained or formally charged.

Economy Minister Zafer Caglayan, Interior Minister Muammer Guler and Environment Minister Erdogan Bayraktar resigned earlier on Wednesday over a high-level corruption crackdown in which sons of the ministers and renowned businessmen were arrested.

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.

The call came as demonstrators took to the streets of Istanbul to protest against the government over the corruption allegations.

Smoke grenades

Protesters chanted slogans as they called for the government to resign.

The rally turned violent when riot police used smoke grenades and water cannon on bottle-hurling demonstrators.

On Thursday prosecutor Muammer Akkas said he had been removed from the case and accused police of refusing to comply with his orders to take more suspects into custody.

"By means of the police force, the judiciary was subjected to open pressure, and the execution of court order was obstructed." he said.

"A crime has been committed throughtout the chain of command... suspects have been allowed to take precautions, flee and tamper with the evidence." 

The high-level 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.

Erdogan called the arrests a "dirty operation" aimed at smearing his administration and undermining the country's progress.

The government reshuffled the police force hours after the investigation was revealed, moving dozens of senior police officers, including the Istanbul police chief, to passive positions over Ankara's claims of "abuse of office".

The investigations are widely believed to be linked to the recent tensions between the US-based Turkish cleric Fethullah Gulen's movement and Erdogan's AKP party.

Gulen was previously a key backer of the AKP, helping it to win three elections in a row since 2002.

The tensions, which have been festering for months, are thought to be linked to government plans to abolish private preparatory schools. Gulen owns a large network of such schools.

Erdogan recently said that those behind the investigations were trying to form a "state within a state", an apparent reference to Gulen's movement, whose followers are influential in Turkey's police and judiciary.

Source: Al Jazeera and agencies