Britain, France, Germany and the United States had asked a UN Security Council sanctions committee to investigate the launch of the Emad missile on October 10.
"On the basis of its analysis and findings, the panel concludes that Emad launch is a violation by Iran of paragraph 9 of Security Council resolution 1929", said the 11-page report obtained by AFP.
Adopted in 2010, Resolution 1929 prohibits Tehran from conducting launches of ballistic missiles capable of delivering nuclear weapons.
Iran had denied that the missile launch was in violation of the resolution, with Foreign Minister Mohammad Javad Zarif saying that it was not designed to carry nuclear warheads.
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Iran insists it has no plans to develop atomic weapons.
The finding from the panel could trigger moves to impose sanctions on Iran for violating the resolution, although such a decision would require agreement from China and Russia.
British Ambassador Matthew Rycroft said the report would be discussed at a Security Council meeting later Tuesday.
Rycroft stressed the importance for the United States, especially the US Congress, that the council "does respond effectively to what appears to be a breach, not of the JCPOA, but of previous resolutions."
The JCPOA is the Joint Comprehensive Plan of Action, the international agreement reached with Iran in July on ending the standoff over its alleged nuclear ambitions.
"Entities involved in launches like the one concluded on October 10th have already been designated under existing sanctions, which we will continue to fully enforce going forward," said the official.
"These entities will not be let off the hook for their involvement in Iran's ballistic missile program," he said.
The United States is also looking at reports of a new ballistic missile test on November 24.