A supporter of Gulen movement holds a Turkey's national flag during a protest outside the Kanalturk and Bugun TV building in Istanbul, Turkey, October 28, 2015. REUTERS/Osman Orsal

By Daren Butler

ISTANBUL (Reuters) - Turkish police detained dozens of people including senior police officers and bureaucrats allegedly linked to President Tayyip Erdogan's foe Fethullah Gulen on Tuesday, widening a campaign against the exiled Muslim cleric after Sunday's election.

The prosecutor's office in the western city of Izmir said it ordered the arrest of 57 people believed to be members of the "Gulenist terror group", on allegations they sought a purge of the army by engineering a 2012 espionage trial.

Gulen was the "number one" suspect in the latest investigation, according to the Dogan news agency.

The operation came two days after the AK Party, which Erdogan founded, secured a return to single-party rule, in an election result he portrayed as a vote for stability but which opponents fear heralds growing authoritarianism.

Police detained 44 of the suspects in dawn raids, including a former Izmir police chief and three state governors, in an operation covering 18 provinces, state-run Anadolu Agency said. Arrest warrants were issued for the other 13.

The 2012 espionage case involved the trial of 357 people, including soldiers, accused of possessing secret military information and documents. Those defendants have been released but the case continues.

The Izmir prosecutor's office said in a statement there was "serious evidence" that the 57 suspects sought to use the 2012 case to orchestrate a purge in the state bureaucracy and the military.

During his early years as prime minister, Erdogan sought to tame the power of an army which had dominated Turkish politics for decades. Gulen, then his ally, was widely held to have helped in the process through his influence in the judiciary.

The drive was epitomized by high-profile trials of those who allegedly plotted to overthrow his government. Officials suggest those cases were brought by police and prosecutors close to Gulen. Gulen denies such allegations.

Erdogan turned against Gulen and launched a crackdown against his followers after police and prosecutors seen as sympathetic to the cleric opened a corruption investigation into Erdogan's inner circle in 2013.

The cleric has lived in exile in the United States since 1999 and is himself the subject of arrest warrants in Turkey. A prosecutor is seeking a prison sentence of up to 34 years on allegations that he sought to topple Erdogan. Gulen also denies that allegation.

Erdogan's campaign against Gulen continued in the months leading up to Sunday's election. On Oct. 27, Turkish authorities took over the management of companies including newspapers and TV stations linked to the cleric.

(Writing by Daren Butler; Editing by Nick Tattersall, David Dolan and Raissa Kasolowsky)