Morgan, who took over the England captaincy from Alastair Cook last month, moved to end speculation surrounding the future of the maverick batsman, sacked by England last February.
Pietersen renewed speculation during a television interview this week with former Australia captain Ricky Ponting during a Big Bash League match when he claimed Morgan wanted to have him back in England's 50-over team.
While the pair are friends, Morgan put paid to outside hopes Pietersen may have had of returning to England's World Cup squad as an injury replacement.
England take on Australia in the opening match of the tri-series in Sydney on Friday in a tournament also involving India and Morgan laid his cards out on the table.
"I think this is a good opportunity to clear things up given that Kevin has a lot of opportunity to talk in the media and get his point of view out there," Morgan told travelling English reporters.
"I'm very happy with the group of players I have, I think this is the best group of players we have to drive the England team forward over the next two months in particular.
"Kevin's situation hasn't changed over the last year. It's been reiterated over months and days.
"It was reiterated before Christmas by the chairman of selectors and I'm reiterating it again just to clear it up. Thank you."
Of more pressing concern for Morgan was the fitness of star fast bowler James Anderson as he recovers from a knee injury.
Anderson looked fit in his return to the team in their 216-run hammering of a local side in Canberra on Monday, but sat out Wednesday's win over the Prime Minister's XI.
Morgan said the decision was made to rest their spearhead to give him the best possible chance to play in Friday's tri-series opener.
"It was more managing his workload coming back from injury," Morgan told reporters.
"We decided that he wouldn't be able to play three games in a week and obviously the most important game is tomorrow.
"So in order for him to be fit for selection, we needed to up his workload in the nets. And if he had have played yesterday he wouldn't have pulled up that well."
Anderson was put through a full practice session Thursday with Morgan saying "we'll see how he pulls up tomorrow morning".
He added that Anderson was the only injury concern heading into the one-day international.
"Everybody else is, to my knowledge, at the moment fit for selection."
Morgan praised Ian Bell's 187-run knock against the Prime Minister's XI, the highest innings by an England batsman in a competitive 50-over match, and said it epitomised the ruthlessness his side needed to succeed.
Their first priority was to beat India and Australia in the tri-series as a confidence-booster heading into next month's World Cup.
"It'll be nice to be sitting here at the end of this series with some silverware and very confident in where we're going as a side," Morgan said.
"I know throughout this series it might throw up a couple of things because Australia can be a difficult place to tour, a difficult place to adapt to conditions, but I certainly think that we're one of the sides that finds it a lot easier to adapt.
"They are conditions that suit our game and we proved that a bit yesterday.
"Mindset and method-wise, we're in a good place — particularly with our batting."
Like Sports on Facebook, follow @ETribuneSports on Twitter to stay informed and join in the conversation.
COMMENTS
Comments are moderated and generally will be posted if they are on-topic and not abusive.
For more information, please see our Comments FAQ