The son of Turkey's prime minister will likely be the next target of a widening graft probe that led to a major cabinet reshuffle after three ministers resigned, Turkish media said Thursday.

Several newspapers said a bitter struggle between Prime Minister Recep Tayyip Erdogan and his one-time ally turned opponent Fethullah Gulen was set to become more venomous as the corruption scandal inches closer to the premier's inner circle.

The opposition Cumhuriyet daily predicted an “earthquake” as investigators turn their attention to an NGO connected to the premier's son Bilal.

The paper said prosecutors were pressuring police to investigate construction tenders granted to the NGO by an Istanbul municipality, whose mayor has been implicated the corruption scandal.

The mayor, a member of Erdogan's Islamic-rooted Justice and Development Party (AKP), was briefly detained last week but later released pending trial.

Three ministers also resigned this week over the corruption inquiry, two of them after their sons were taken into custody.

Erdogan on Wednesday announced a major cabinet reshuffle after the resignations.
But there was no sign that he himself would step down as demanded by anti-government protesters as well as by the environment minister who resigned.

Observers say the graft probe is the result of a rift between Erdogan and Gulen, an Islamic scholar who has lived in self-imposed exile in the United States since 1999.
Gulen's followers hold senior positions in the Turkish judiciary and police.

Erdogan's government, which weathered mass street protests in June, has been embroiled in a bitter dispute with Gulen's backers over plans to shut down a network of schools run by the movement.
The struggle between the two men poses the biggest threat to Erdogan's undeclared ambition to run for president in 2014.

There is not even a little sign of a ceasefire, let alone peace,” columnist Rusen Cakir wrote in the Vatan daily on Thursday. “To the contrary, it appears the battle (between Erdogan and Gulen) will turn even more violent.”

“It is obvious that the (Gulen) movement have more tricks up their sleeve,” he predicted.

Gulenists have their own media, universities, think-tanks, and businesses, and with their followers in key positions, analysts say, the movement appears to be the only force that can challenge Erdogan in the run up to local polls in March.

“If the government rushes to act with hostility and moves ahead with hurtful (police) sackings, it will open deep wounds ... which will not be forgotten for centuries,” Ali Bulac wrote in the Zaman daily, which is affiliated with the Gulen movement.

Erdogan's Justice and Development Party (AKP) has dominated politics for 11 years and won three successive elections, gaining almost 50 percent of the vote in 2011 after presiding over steady economic growth.