* Erdogan replaces half of ministers amid graft scandal
* New official overseeing police considered tough on unrest
By Dan Williams
ISTANBUL, Dec 26 (Reuters) - Turkey's opposition accused scandal-hit Prime Minister Tayyip Erdogan on Thursday of trying to rule via a secretive "deep state", after a cabinet reshuffle that would tighten controls on police already beleaguered by government-ordered purges.
Among 10 new loyalist ministers Erdogan named late on Wednesday was Efkan Ala, a former governor of the restive Diyarbakir province who will wield the powerful Interior portfolio and oversee Turkish domestic security.
Ala replaces Muammer Guler, one of three cabinet members who resigned after their sons were detained in a graft probe that erupted on Dec. 17. Guler, who like Erdogan had called the case baseless and a plot, sacked or reassigned dozens of police officers involved including the chief of the force in Istanbul.
"He (Erdogan) is trying to put together a cabinet that will not show any opposition to him. In this context, Efkan Ala has a key role," Kemal Kilicdaroglu, the head of the biggest opposition party CHP, said in remarks carried by Turkish media.
"Erdogan has a deep state, (his) AK Party has a deep state and Efkan Ala is one of the elements of that deep state," added Kilicdaroglu, using a term that for Turks denotes a shadowy power structure unhindered by democratic checks and balances.
During his three terms in office, the Islamist-rooted Erdogan has transformed Turkey, cutting back its once-dominant secularist military and overseeing rapid economic expansion. He weathered unprecedented anti-government protests that swept major cities in mid-2013.
But the corruption scandal has drawn an EU call for the independence of Turkey's judiciary to be safeguarded and has rattled stocks and the lira, with the currency falling to a historical low of 2.1025 against the dollar on Monday.
The affair is a potent and personal one for Erdogan.
It lays bare his rivalry with Fethullah Gulen, a U.S.-based Turkish cleric whose Hizmet (Service) movement claims at least a million faithful including senior police officers and judges.
Another of the three cabinet members who quit on Wednesday over their sons' detention, Environment Minister Erdogan Bayraktar, broke ranks by urging the premier to follow suit.
The Turkish leader, in power for 11 years and facing local elections in March and a national ballot in 2015, was unmoved. Vowing no tolerance for corruption, he said on Wednesday graft investigation was tainted by foreign interests.
Unlike anyone else in the 20-member cabinet, Ala is not a member of parliament and thus does not answer directly to a constituency.
In his previous post as undersecretary of the prime ministry, political sources told Reuters, he urged a crackdown on demonstrators who flooded the streets over the summer in protest at what they see as Erdogan's authoritarianism.
"Who would you trust other than your undersecretary, with whom you have been working closely for years?" said one government source, who characterised the new ministers as "surprise" picks conveying Erdogan's desire for fresh faces. (Additional reporting by Humeyra Pamuk and Orhan Coskun; Writing by Dan Williams; Editing by Andrew Roche)