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Media tycoon Rupert Murdoch has questioned the "sense of proportion" and time taken by police investigating phone-hacking claims in a letter to MPs.

He retracted accusations made on a secret tape recording that police were "totally incompetent" but said the length of time police were taking between arresting and charging suspects had led to suicide attempts.

Murdoch was responding to a request from Home Affairs Select Committee chairman Keith Vaz to explain the recorded comments, which he believed he was making in private to journalists from his Sun newspaper.

"I accept that I used the wrong adjectives to voice my frustration over the course of the police investigation," wrote the 82-year-old businessman in a letter.

"I am in no position to judge the competence of the investigation and should never have done so."

But he later criticised the manpower and time being consumed by investigations into behaviour at his News International titles.

"My own lay view is that it has been more than thorough, indeed it has in some respects appeared to be excessive," he argued.

"My own personal view is that this has gone on too long.

"I cannot endorse the judgement that the investigation has 'progressed' very well, not when some of our employees were arrested early in the investigation in 2012 and their families are still in limbo".

Murdoch said that the stress on families had led to "suicide attempts and medical conditions".

Vaz welcomed Murdoch's "acceptance that he used the wrong words to describe the police investigation and his explanation of why he did so."

"I am glad that he has confirmed he does not think the police investigations are incompetent," he added.

He also echoed Murdoch's fears about the cost of the investigation, which so far stands at ??20.3million ($30.9 million, 23.5 million euros).

On the recording, the tycoon appears to call the probes into phone hacking and bribery by his journalists a "disgrace".

He was speaking in March at a meeting with journalists at his top-selling British tabloid The Sun, where he also appeared to suggest that reporters jailed as a result of the probe could get their jobs back.

According to the tape obtained by the Exaro investigative website and released by Channel 4 news, Murdoch said his News Corporation made a "mistake" in handing over so much information to police.

Murdoch shut down his top-selling News of the World tabloid in July 2011 after it emerged the weekly had illegally accessed the voicemails of hundreds of public figures, including murdered teenager Milly Dowler.

Hauled before British MPs to explain himself over the scandal, Murdoch apologised and said "this is the most humble day of my life".

But in the meeting this year, which was apparently secretly recorded by one of his own journalists, Murdoch was defiant, railing against the ongoing police investigations into hacking and the alleged bribery of public officials.

He has divided New York-based News Corp since the hacking scandal into two companies separating the television and film business and the newspaper and publishing arm.