Upon announcing his international retirement, Berbatov said: "I am going nowhere.
"I have arrived where I wanted to be, I have reached the summit."
Berbatov has come under fire this season from fans critical of his work-rate and profligacy in front of goal.
He did not start a single match in the Champions League knockout stages before United were knocked out by Bayern Munich in the last eight.
Critics have also suggested United lost the Premier League title to Chelsea in part because of his failure to act as an effective replacement for Wayne Rooney during the England striker's injury absence.
Berbatov, though, insisted he is determined to stay, adding: "United is the biggest team and I will fight to stay there until the end of my contract."
His current deal expires in two seasons' time in 2012.
While the Bulgarian appears content to shrug off criticism for his domestic performances, similar analysis of his international performances have played their part in his decision to quit the national team.
"I have decided to step down from the national team, starting today," he told a press conference in the Bulgarian capital Sofia, adding he wanted "to give younger players the opportunity to step out from my shadow".
Berbatov, Bulgaria's captain for the last three years, scored 48 goals in 74 international appearances and is the nation's all-time leading scorer.
But he said he was "discouraged" by Bulgaria's failure to qualify for the upcoming World Cup in South Africa, adding: "At times I feel tired, even exhausted by the national team."
It means the front man's appearance in the 2-0 defeat in Poland in March was his last at international level.
Another star player - Dimitar Ivanov - also announced his decision to quit international football following that game in Warsaw.
Bulgaria have been drawn in the same Euro 2012 qualifying group as England and Wales.
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