Prime Minister Tayyip Erdogan denounced “international groups” and “dark alliances” yesterday for entangling Turkey in a corruption scandal that has exposed deep rifts between him and a US-based Muslim cleric who helped him rise to power.

Sixteen people, including the sons of two ministers and the head of state-owned Halkbank, were formally arrested yesterday in a corruption inquiry Erdogan has called a “dirty operation” to underminine his rule.

This is an operation ordered by some international groups

The Turkish leader raised the stakes by accusing unnamed foreign ambassadors of “provocative actions”. Some pro-government newspapers had accused the US envoy of encouraging the move against Halkbank – a charge denied by the embassy. “There are extremely dirty alliances in this set-up, dark alliances that can’t tolerate the new Turkey, the big Turkey,” Erdogan in a speech in the northern town of Fatsa. “Turkey has never been subjected to such an immoral attack.”

The furore, which has roiled markets, is seen as reflecting a power struggle between Erdogan and his former ally Fethullah Gulen, who wields influence in the police and judiciary.

Dozens of police chiefs have been removed from their posts since the detentions of bribery suspects began.

“Those who don’t see the thief but go after those trying to catch the thief, who don’t see the murder but try to defame others by accusing innocent people - let God bring fire to their houses, ruin their homes, break their unity,” Gulen said in a recording uploaded to one of his websites on Friday.

Erdogan has refrained from naming Gulen as the hand behind the investigation when he blamed an internationally-backed conspiracy. But Gulen’s Hizmet (or Service) movement has been increasingly at odds with the Prime Minister in recent months.

“This is an operation ordered by some international groups, and their subcontractors within Turkey are carrying it out, as a step taken against the government. We will not bow down to it,” Erdogan said yesterday.