Turkey's Prime Minister Tayyip Erdogan greets members of his ruling Justice and Development Party at a meeting at its headquarters in Ankara on Wednesday. Umit Bekras / Reuters

Turkish Prime Minister Tayyip Erdogan reshuffled his Cabinet on Wednesday after three members quit over a corruption scandal that has posed an unprecedented challenge to his 11-year rule.

The crisis erupted on Dec 17 when dozens of people, including the head of state-run lender Halkbank, were arrested on graft charges. Erdogan responded by purging police investigators. The ensuing feud with the judiciary reignited long-simmering street protests and rattled foreign investors.

Earlier on Wednesday, three ministers who had sons among those detained resigned. Two of them echoed Erdogan in depicting the inquiry as baseless and a conspiracy. The third, Environment Minister Erdogan Bayraktar, turned on the premier.

"For the sake of the well-being of this nation and country, I believe the prime minister should resign," he told NTV news.

By breaking ranks, Bayraktar may have diluted any easing of pressure on Erdogan afforded by the ministers' resignations, although some commentators thought their timing was off.

"These are very late and difficult resignations. They don't have any value in terms of democracy," said Koray Caliskan, an associate professor at Istanbul's Bogazici University.

After nightfall, a spent-looking Erdogan announced he was appointing 10 new ministers to replace the three who quit and others planning mayoral runs in local elections in March.

The fact that the shake-up happened over Christmas cushioned the blow to Turkey on dormant international markets. But the stock index closed 4.2 percent down and the lira weakened to 2.0862 against the dollar.

During his three terms in office, Erdogan has transformed Turkey by tackling its once-dominant secular military and overseen rapid economic expansion. He weathered anti-government demonstrations that swept Istanbul and other cities in mid-2013.

The gauntlet thrown down by Bayraktar set off fresh protests in Ankara, Istanbul and Izmir. Erdogan was unmoved.

Protocol, purges

In a speech earlier on Wednesday, he vowed there would be no tolerance of corruption. He argued that the work of the about 70 police investigators he had sacked or reassigned - including the chief of the force in Istanbul, Halkbank's headquarters - was deeply tainted.

"If a verdict is made by the opposition party on the second day of the investigation, what's the point of having judges? If a decision is made by the media, what's the point of having these long legal procedures?" Erdogan said to provincial leaders of his Justice and Development Party.

Alluding to TV news reports that have riveted Turks with footage of cash-filled shoe boxes allegedly seized at suspects' homes, he asked: "How do you know what that money is for?"

The 14-month investigation was conducted largely in secret. At the weekend, the government changed regulations for the police, requiring officers to report evidence, investigations, arrests and complaints to commanding officers and prosecutors. Journalists have been banned from police stations.

The Hurriyet newspaper said up to 550 police officers, including senior commanders, had been dismissed nationwide in the past week by Interior Minister Muammer Guler, who has now resigned.

Reuters