"It was a difficult decision but sometimes we have to take difficult decisions," the 29-year old Manchester United striker told a news conference at the Vasil Levski national stadium on Thursday.
"I needed a long time but there's no way back. It's over," said Berbatov, who became Bulgaria's all-time leading scorer last November when he netted his 48th goal in a friendly against Malta on his 74th international appearance.
"There are many reasons behind my decision but I want to say I took it on my own and no one influenced it," added the player who was voted Bulgaria's Footballer of the Year for a record sixth time in January.
"I didn't discuss it with (United manager) Alex Ferguson. I did it with my father and my agent."
"I felt tired at times and I also know there are skilful young lads in the national team who look forward to their chance," Berbatov added.
"You have to know when it's the right time to stop. Things have changed a lot since I was a 20-year-old. I have a family, a daughter now..."
His decision is a stunning blow for Bulgaria coach Stanimir Stoilov who has an uphill task in trying to qualify the Balkan country for the European Championship finals in 2012.
Bulgaria have been drawn with England, Switzerland, Wales and Montenegro in Group G with the first matches scheduled for September 3 when they visit Wembley Stadium.
CRITICAL FANS
"I've already informed him (Stoilov) and I wished him success as I also think he's capable of achieving something big with the national team," said Berbatov."
He had been named in Bulgaria's squad for friendlies in Belgium on May 19 and World Cup hosts South Africa on May 24.
However, Berbatov has been criticised by his country's fans for not playing at his best for the national team and Bulgarian Football Union (BFU) vice-president Yordan Lechkov scolded him recently for "not giving enough on the pitch".
The laid-back striker joined United from Tottenham Hotspur in 2008 for a club record fee of 30.75 million pounds but soon came under fire from British media and United supporters after failing to reproduce his scoring form.
But he said on Thursday he was happy at United, who finished runners-up to Chelsea in the Premier League this year, and wanted to remain at the Old Trafford club.
"I'm a Man United player, I want to stay there and I'll fight for my place. I wake up happy every morning because I know I'm a United player. I don't show my emotions but that doesn't mean I'm not happy."
Asked about speculation he could leave United, Berbatov said: "I don't know anything about an offer from Milan or from any other club. Germany? There's only one team I could play for there and it's Bayer Leverkusen (his former club)."
Berbatov is the second key Bulgarian player to retire from international football this year after Bursaspor goalkeeper Dimitar Ivankov quit after a friendly against Poland in March.
"It's a sad news for all of us because no doubt Berbatov is one the most successful Bulgarian players," said Bul
