"He (Pietersen) has been fined an undisclosed sum in accordance with the terms and conditions of his England Central Contract, while Mascarenhas, the Hampshire captain, was fined £1,000 by his county and faces a further rap from the ECB after branding national selector Geoff Miller 'a k***' and 'a p****' on Sunday," the ECB said in a statement.
Rod Bransgrove, the Hampshire chairman, said: "I met with Dimitri Mascarenhas today and formally censured him, imposing a fine of £1,000. The fine has been set at this high level as I feel there is little point in imposing a ban, given the long-term nature of his injury.
Pietersen had posted a Twitter message last Tuesday announcing that he had been dropped for the One-day series at home to Pakistan. The message contained an expletive.
Pietersen's punishment was decided after an ECB disciplinary hearing at Lord's convened by Hugh Morris, Managing Director of England Cricket and England team director Andy Flower [ Images ].
"The hearing considered two charges against Kevin Pietersen relating to recent comments made on Twitter following his omission from England's one-day squad for the series against Pakistan," the statement said.
"Pietersen pleaded guilty to both charges and offered an unreserved apology to ECB and the England team management for his actions."
The former England captain apologised publicly last Wednesday, insisting on Surrey TV that his comments "had not been for the public domain".
The ECB said Pietersen had been dropped so that he could regain some form with county side Surrey after a run of disappointing scores.
Meanwhile, Mascarenhas said that it was irresponsible on his part to have tweeted. "I realise that my actions were stupid and irresponsible and I regret any offence I may have caused. I apologise specifically to Geoff Miller, who has always treated me fairly. I also apologise to Hampshire Cricket, whom I feel I have let down. This was a silly, late-night conversation that got out of control and doesn't reflect my true views on Mr Miller," Mascarenhas said.