The Sunday Times reports that the ECB is seeking to confirm whether Pietersen's texts went beyond banter and into the realm of betrayal of his captain.
Pietersen has claimed that the texts to South African stars including Morne Morkel and Dale Steyn were merely "banter", but the newspaper reports that one of the texts apparently told the Proteas duo that the best way to dismiss Strauss is by bowling round the wicket.
Morkel bowled round the wicket to take Strauss's wicket in the first Test at The Oval, while Steyn dismissed the England captain using the same tactic at the second Test at Headingley.
The Sunday Times report adds that Pietersen's relationship with Strauss had been more stormy than previously thought even before the text scandal, claiming that, "the two men were seen in a vigorous argument three days before the start of the South Africa series."
South African cricket officials have told the ECB that the texts were indeed banter, but the newspaper reports that the ECB will not accept Pietersen's apology until the full content of the messages is known.