* Law targets schools run by Muslim cleric Gulen
* PM accuses former ally Gulen of seeking to topple him
ANKARA, March 12 (Reuters) - Turkish President Abdullah Gul approved on Wednesday a law closing private preparatory schools, many of which are a source of income and influence for an Islamic cleric accused by Prime Minister Tayyip Erdogan of seeking to topple him.
The move highlights Gul's solidarity with Erdogan as the prime minister battles a corruption scandal he says has been orchestrated by the cleric, Fethullah Gulen, whose "Hizmet" (Service) network wields influence in the police and judiciary.
Education is central to the mission of Gulen's movement. Millions of students prepare at the cram centres for entrance examinations to win limited spots at state high schools and universities.
Tensions between Erdogan and the U.S.-based cleric, formerly allies, have been simmering for years but boiled over when the graft scandal erupted in December with the detention of three ministers' sons and businessmen close to the prime minister.
The scandal, which Erdogan has cast as a plot to oust him by a "parallel state" of Gulen's followers, came weeks after the government moved to shut down the prep schools, worsening the public row with the cleric's followers.
Parliament voted earlier this month to close the schools by Sept. 1, 2015 but the move was subject to the approval of Gul, a figure seen by many in Turkey as having been closer to the Gulen movement than the prime minister.
Erdogan, currently campaigning around the country for municipal elections on March 30, has responded to the corruption scandal by reassigning thousands of police officers and hundreds of judges and prosecutors in what his aides have described as a bid to cleanse the judiciary of Gulen's influence.
Gulen's followers say they are the victims of a witch hunt.
(Reporting by Gulsen Solaker; Writing by Nick Tattersall; Editing by Gareth Jones)