"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..."
"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".
"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)."
"It's a sad news for all of us because no doubt Berbatov is one the most successful Bulgarian players," said Bul
