"Iran will be at the World Cup," Infantino said at half-time of Iran's friendly against Costa Rica in Turkey.
"That's why we're here. We're delighted because they're a very, very strong team, I'm very happy."
"I've seen the team, I've spoken to the players and the coach, so everything is fine," added Infantino, whose attendance at Tuesday's game was unannounced.
Infantino went on to stress that Iran's "matches will be played where they are supposed to be, according to the draw".
The World Cup, being hosted by the United States, Mexico and Canada, starts on June 11.
Iran are set to play their first Group G game against New Zealand in Los Angeles on June 15. They are then scheduled to play Belgium in Los Angeles on June 21 and Egypt in Seattle on June 27.
Iran's participation had been thrown into doubt by the war with the US and Israel that broke out on February 28.
The Iranian football federation said earlier this month it was "negotiating" with FIFA to relocate the country's World Cup matches from the United States to Mexico.
Mexican President Claudia Sheinbaum also said that her country is prepared to host Iran's first-round matches at the tournament if needed.
Infantino initially said that US President Donald Trump had given assurances that the Iranian team would still be welcome.
But Trump then stated that Iran's team should not travel to the tournament "for their own life and safety".
Iran hit back at Trump's comments, saying that "no one can exclude Iran's national team from the World Cup".
On March 19, Infantino said FIFA was committed to making sure the World Cup goes ahead "as scheduled" with "all teams" taking part.
"FIFA is looking forward to all teams participating at the World Cup to compete in a spirit of fair play and mutual respect," Infantino said from Zurich during an online FIFA Council meeting.
"FIFA can't solve geopolitical conflicts, but we are committed to using the power of football and the World Cup to build bridges and promote peace as our thoughts are with those who are suffering as a consequence of the ongoing wars," added Infantino.
Iran also played a friendly against Nigeria in Turkish town Belek last Friday.
Iran's players wore black armbands and posed with school rucksacks as the national anthem played to remember the victims of a strike on a primary school in Iran on the first day of the Middle East war.
The airstrike on the school in the southern Iranian city of Minab on February 28 killed at least 170 people including students and teachers.
The New York Times has reported that the preliminary findings of a US military investigation indicate that a US Tomahawk cruise missile hit the school due to a targeting mistake.
