"It's a reality that today is my last match with the national team. At the individual level, a wonderful stage ends," the hero of Spain's only World Cup championship in 2010 told reporters at Moscow's Luzhniki Stadium, reports Efe.
"It's a shame we couldn't go through. Penalties are cruel. The guilty ones are always the players and everyone of us is responsible," he added.
"Overall it's probably the saddest day of my career. I leave with a bad taste in my mouth.AIt's tough for everybody, the 34-year-old midfielder said, acknowledging his disappointment about losing to underdogs Russia on penalty kicks.
With 13 goals in 131 appearances for Spain, Iniesta was a vital part of the La Roja side that claimed the 2008 and 2012 European Championships as well as the 2010 World Cup, where he scored the winning goal.
Iniesta declined to second-guess coach Fernando Hierro's decision to leave him on the bench until past the one-hour mark of Sunday's match.
"The coach is the one who makes the decision, beyond whether one agrees or not," Iniesta said. "At the end, the coach looks at what's best for the team, and that's how I understood it," he added, reports Xinhua news agency.
Iniesta said the players could not blame turbulence off the pitch for their failure to live up to expectations. "It would be wrong to say that (coach Julen Lopetegui's) dismissal was fundamental," he said.
"Everything has its importance. But in the end, we are the ones who have the ball."
Iniesta, who will play for Japanese club Vissel Kobe next season after ending his 22-year FC Barcelona career in May, is confident Spain can rebuild ahead of the next World Cup in Qatar.
"There are players around, they just have to find a path to success," he said. "It's not easy and harder than it appears. But the national team will keep going there are players who have a good level."