Pietersen confirmed that he would no longer play for England last Tuesday after the South Africa-born batsman was left out of the England squads for the tour of the Caribbean and the ICC World Twenty20.
At the time, the ECB would only cite the need for a new "team ethic and philosophy" in the wake of the 5-0 Test series defeat in Australia.
However, following calls for an explanation from players including former England captains Ian Botham and Michael Vaughan, the ECB issued a joint statement with the Professional Cricketers' Association.
"The ECB recognises the significant contribution Kevin has made to England teams over the last decade," the statement read yesterday.
"He has played some of the finest innings ever produced by an England batsman. However, the England team needs to rebuild after the whitewash in Australia.
"To do that we must invest in our captain Alastair Cook and we must support him in creating a culture in which we can be confident he will have the full support of all players, with everyone pulling in the same direction and able to trust each other.
"It is for those reasons that we have decided to move on without Kevin Pietersen."
Pietersen, 33, bowed out as England's record scorer across all formats of the game, with 13,797 runs to his name.
However, his strong personality made him a divisive presence in the England changing room.
He fell out with two head coaches in Peter Moores and Andy Flower and was also briefly dropped in 2012 after it emerged that he had sent text messages criticising then England captain Andrew Strauss to South African players.
The ECB went on to address accusations emanating from social media that Pietersen had been forced out of the England squad by figures from within the camp.
"Allegations have been made, some from people outside cricket, which as well as attacking the rationale of the ECB's decision-making, have questioned, without justification, the integrity of the (former) England team director (Flower) and some of England's players," the statement added.
"It is important to stress that Andy Flower, Alastair Cook and (wicketkeeper) Matt Prior, who have all been singled out for uninformed and unwarranted criticism, retain the total confidence and respect of all the other members of the Ashes party.
"These are men who care deeply about the fortunes of the England team and its image, and it is ironic that they were the people who led the reintegration of Kevin Pietersen into the England squad in 2012."
Speaking before the ECB explained its reasons for deciding to jettison Pietersen, Strauss had expressed a belief that trust was the critical issue.
"Without trust, the team environment is stillborn. It is for this reason that Kevin Pietersen's international career had to be brought to an end," Strauss wrote in British newspaper the Sunday Times.
"The media have been searching for a 'smoking gun'. Everyone is looking for disciplinary problems, bust-ups and character clashes, but they are looking for the wrong thing.
"The smoking gun is the total absence of trust."