* Ruling party seeks tighter control over judiciary
* Top judicial body says plans are unconstitutional
* Separate draft seeks tighter internet controls
By Orhan Coskun
ANKARA, Jan 10 (Reuters) - One of Turkey's most senior legal figures warned Prime Minister Tayyip Erdogan's AK Party on Friday that efforts to tighten its grip on the judiciary would breach the constitution, deepening a crisis triggered by a damaging corruption scandal.
Erdogan has cast a wide-ranging graft investigation, which poses one of the biggest challenges of his 11-year rule, as an attempted "judicial coup" and has responded by purging the police force of hundreds of officers and seeking tighter control over judicial appointments.
His AK Party unveiled plans this week, due to be discussed by parliament's justice commission, to give government more say over the appointment of judges and prosecutors, rolling back reforms championed by the European Union.
"These regulations concerning the independence and impartiality of judges ... will be in contravention of the constitution," said Ahmet Hamsici, deputy chairman of the High Council of Judges and Prosecutors (HSYK), in a 66-page report.
"It is clear that this situation represents a contravention of the principle of judicial independence (and) the separation of powers," said the report, submitted on Friday to the parliamentary commission and seen by Reuters.
The AKP bill, published on parliament's website, proposes changes to the structure of the HSYK, the body responsible for appointments in the judiciary, which would give the justice minister greater power over its activities.
Erdogan's supporters have cast the corruption probe as a smear campaign contrived, ahead of elections this year, by a U.S.-based Islamic cleric, Fethullah Gulen, who exercises broad, if covert, influence in the judiciary and media.
The affair, exposing a deep rift within the Turkish political establishment, has driven the lira to new lows and shaken investor confidence in a country whose stability has largely derived from Erdogan's strong grip on power.
But it is the government's reaction, seeking tighter control over the judiciary, police and even the internet, which risks doing the deepest long-term damage, not least to Turkey's ambitions to join the European Union and to its relations with Washington, already critical of its record on human rights.
"We've expressed our concerns about some of the events that are happening on the ground directly, publicly and privately, and we'll continue to do that," U.S. State Department spokeswoman Jen Psaki said on Thursday, saying the U.S. backed the Turkish people's desire for a transparent legal system.
Nils Muiznieks, commissioner for human rights at the Council of Europe, said on Twitter that the proposals for changes to the HSYK represented a "serious setback for the independence of the judiciary in Turkey".
The ruling party did not immediately respond to Hamsici's report but has been critical of previous statements from the HSYK regarding the handling of the corruption investigation.
The AKP also submitted a draft bill to parliament this week seeking tighter control over the internet, allowing authorities to block access to a website deemed inappropriate within 48 hours, more quickly than current regulations allow.
The proposal would allow the authorities to keep internet records of individuals for up to two years, including their browsing and search histories.
Erdogan's government blamed social media for helping orchestrate weeks of anti-government demonstrations last summer, although the AK Party also encouraged its members and supporters to mount a counter-offensive on Twitter.
"This thing called social media, I think, is right now a menace to society," Erdogan said in a TV interview last June.
Turkey already has tight internet controls. Video streaming service Vimeo was shut down in Turkey on Thursday, a statement on its website saying a court ordered its closure on Jan. 8.
Mehmet Ali Koksal, a lawyer for Turkey's TBD information technology association, said the draft bill had been prompted by fears of more revelations in the corruption investigation.
"There's an expectation that more videos, pictures related to the scandal could become public," he said.
AKP deputies who signed the draft bill did not immediately respond to phone calls seeking comment.
Both of the ruling party bills must be voted on by parliament before being sent for approval to President Abdullah Gul, who has largely kept out of the row but has repeatedly stressed the need for the separation of powers.
Veteran columnist Cengiz Candar said he hoped even some AKP members of parliament would challenge the bill on the judiciary.
"Leaving aside the legality, this is an unethical step," he wrote in the liberal daily Radikal on Friday.
"One has to believe that there are parliamentarians within the AKP who have not lost their ethics and common sense and who can be expected to come out against this."
(Additional reporting by Daren Butler and Humeyra Pamuk in Istanbul; Writing by Nick Tattersall; Editing by Giles Elgood)