Ambassador Abolfazl Pasandideh visited the northwestern Mexican border city of Tijuana, where Iranians have relocated their training camp. They were originally planned to be based in Tucson in the US state of Arizona.
The ambassador told a news conference that "the country to the north" - meaning the US - had not followed through on its responsibility of hosting the Iranian team.
"We don't know whether or not they're going to give the players their visas," he added.
Iran will play their three World Cup group games in two west coast US cities: Los Angeles and Seattle. The head of the Iranian Football Federation has said they were hoping players would be granted multiple entry visas.
"We aren't participating in the World Cup on equal terms," Pasandideh said.
"We haven't been able to train our team like they should," he said, because of the war in the Middle East that began February 28th.
On Wednesday, Iranian diplomats visited the stadium where the team is training, a source from Club Tijuana that plays there told AFP. The diplomats also met with local security officials, the source said.
Iran are due to play in Los Angeles on June 15th against New Zealand and on June 21st against Belgium, then in Seattle against Egypt on June 26th.