Turkish prosecutors on Wednesday said they had launched an investigation into the national rail authority over corruption claims in public tenders, widening a graft probe that has rocked the government.

The announcement comes after the Cumhuriyet newspaper reported that prosecutors were investigating TCDD (Turkish State Railway) director Suleyman Karaman on charges of "corruption," "tender fraud" and "establishing a criminal organization."

Turkish Prime Minister Recep Tayyip Erdogan saw President Abdullah Gul late Wednesday amid expectations he was about to reshuffle his cabinet following the resignation of three ministers amid a high-level graft scandal.

Gul said Tuesday that Erdogan was preparing to replace several of his ministers. On Wednesday, Turkey's interior, economy and environment ministers quit the government, with the latter also calling on Erdogan to step down.

Turkish Prime Minister Recep Tayyip Erdogan, rattled by a huge corruption scandal implicating some of his closest allies, is preparing a cabinet reshuffle, Turkish President Abdullah Gul said Tuesday.

Gul said the premier, who is on an official visit to Pakistan, is expected to announce the reshuffle after he returns late Tuesday.

At least 10 soldiers drowned on Monday after a tugboat capsized at a military shipyard off western Turkey, Turkish army said.

"Ten of our military personnel died and 17 others were injured when our tugboat TGC Degirmendere capsized," the army said in a statement.

Turkish Prime Minister Recep Tayyip Erdogan is planning a major cabinet reshuffle amid mounting tensions over an anti-graft probe that has touched the heart of the government, local media reported.

Erdogan, who was already expected to reshuffle his cabinet ahead of local elections on March 30, is expected to replace 10 ministers by the end of the month, the Hurriyet newspaper reported.

Turkey's state-owned Halkbank, whose chief executive was arrested in connection with a sweeping graft investigation, said on Monday it complied with the law when doing business with sanctions-hit Iran.

"Our bank's business transactions are regularly audited by relevant authorities," the bank said in a statement.

Turkey's prime minister threw down the gauntlet to his rivals on Sunday, warning them against using allegations of high-level corruption to undermine his rule or he would "break their hands."

"Everyone will know their place," Erdogan told a boisterous crowd of Justice and Development Party (AKP) supporters in the Black Sea province of Giresun.

Turkish Prime Minister Recep Tayyip Erdogan Saturday warned he may expel some foreign ambassadors over "provocative actions", amid mounting tensions over an anti-graft probe that has ensnared government allies.

"Some ambassadors are engaged in provocative actions... Do your job," Erdogan said in televised remarks in the Black Sea city of Samsun. "We don't have to keep you in our country."

Six pro-Kurdish lawmakers on Friday ended a hunger strike they began on Tuesday to denounce court rulings against the release of jailed MPs with suspected links to Kurdish rebels.

"We have ended our action. We hope that our fellow lawmakers will be released," one of the strikers Sebahat Tuncel told journalists.

The sons of two Turkish ministers were charged on Saturday in a huge graft scandal that has ensnared the closest allies of Prime Minister Recep Tayyip Erdogan.

The scandal is the largest ever to come close to Erdogan, who has led Turkey since 2002 as the head of a conservative Islamic-leaning government.