Pietersen quit as captain after just three Tests and nine one-dayers in charge
England captain Kevin Pietersen has quit in the wake of his rift with coach Peter Moores, who has been sacked.
Pietersen said he made the decision "in light of recent communications with the England and Wales Cricket Board (ECB) and the media stories that followed".
"It would be extremely difficult for me to continue in my current position," added the 28-year-old's statement.
Andrew Strauss has been named as captain for the tour of the West Indies, which begins on 21 January.
Hugh Morris, managing director of the ECB, said in a statement that the search for a new coach would begin "immediately".
"This has become an impossible situation given the irretrievable breakdown of the relationship between captain and coach," he added.
"Kevin recognised that in the present situation it was impossible to restore the dressing room unity, which is vital if England are to win the forthcoming tour to the Caribbean, the ICC global events or regain the Ashes in the npower Ashes Test series."
News statement - ECB chief Hugh Morris
Pietersen will, however, continue to play his part as a member of the team, with Morris adding: "I have an extremely high respect and regard for Kevin. He remains highly valued as a senior and experienced player."
News of Pietersen and Moores's departures ended a day of claim, counter-claim and confusion, which began with rumours that the pair had both tendered their resignations.
However, Pietersen, who will return to England from South Africa on Thursday, was keen to set the record straight.
"Contrary to media speculation, I wish to make it very clear that I did not resign as captain of the England cricket team this morning," he said.
Gough blames leaks for Pietersen saga
"But in light of recent communications with the ECB, and the unfortunate media stories and speculation that have subsequently appeared, I now consider that it would be extremely difficult for me to continue in my current position.
"Accordingly, I have as of this afternoon decided to stand down with immediate effect. I still fully intend to be a part of both England's Test and one-day international squad to tour the West Indies next month and to do all I can to recapture the Ashes during the summer."
It has been reported that Pietersen and Moores disagreed over a range of issues, including team selection - most notably that of Michael Vaughan - training regimes and leadership style.
And Pietersen admitted last week his relationship with Moores was strained as they clashed on how to move England forward.
However, the South African-born batsman denied he was at fault for the pair's disagreements being fed to the media, saying: "I have principles in my professional and personal life as to how things are done.
"During my time as England captain I have always been both helpful and direct in my communications with the ECB.
"At no time, contrary to press speculation, have I released any unauthorised information to the media regarding my relationships with the players, coaches and the ECB itself."
Pietersen departs with a record of one win, one draw and one defeat in his three Test matches in charge, while his one-day record as captain reads won four, lost five.
And BBC 5 Live's cricket correspondent Jonathan Agnew says Pietersen's resignation marks "a turnaround" from his position last week when he "first announced he couldn't work with Moores anymore".
"It was a 'back me or sack me' situation he laid down," continued Agnew.
"And effectively, the ECB sacked him last night (Tuesday). There was a late night teleconference between the members of the board and it was concluded that both Pietersen and Moores would be sacked.
"Today, clearly there has been a lot of negotiation and I understand Pietersen is not at all happy with the situation."
Pietersen succeeded Michael Vaughan as England captain on 4 August and led the side to victory in his first Test match in charge against South Africa, following that up with a 4-0 win in the subsequent one-day international series against the tourists.
Pietersen resignation was inevitable - Agnew
But Pietersen's England were crushed by 10 wickets in their Stanford Super Series Twenty20 showdown in Antigua and were then humbled 5-0 by India in a one-day series that was cut short by the Mumbai attacks.
England left the sub-continent in the wake of the attacks, but returned to India for the two-Test series in December, losing one and drawing one.
As for Moores, he lost four out of seven Test series after succeeding Duncan Fletcher as England coach 18 months ago.
England travel to the Caribbean at the end of this month for a Test and one-day series against the West Indies and former captain Graham Gooch, for one, expressed his concern about the effect all this will have on the team.
He told 5 Live: "What really worries me is what's going on in the dressing room.
"There are obviously some factions in the dressing room, some with Pietersen and some not, and that's not the sort of harmony you want before a big series in the West Indies and of course the Ashes.
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