Iran said it conducted a satellite launch but that the rocket failed to reach orbit.
The reported launch, on January 15, came amid growing warnings from the United States about Tehran's rocket tests and accusations that they violate United Nations resolutions.
Telecommunications Minister Mohammad Javad Azari Jahromi told state TV that the rocket carrying the Payam (Message) satellite failed to reach the "necessary speed" in the third stage of launch.
He did not say what caused the failure but vowed that scientists would continue their research.
Israeli Prime Minister Benjamin Netanyahu slammed Iran over the launch, alleging that the "innocent satellite" was actually "the first stage of an intercontinental missile" Iran is developing in violation of international agreements.
Another Iranian satellite named Doosti (Friendship) was waiting to be launched, Azari-Jahromi tweeted after announcing the failed launch.
"We should not come up short or stop," the minister wrote on Twitter. "It's exactly in these circumstances that we Iranians are different than other people in spirit and bravery."
Payam and Doosti were both intended to gather information on environmental change in Iran, President Hassan Rohani said earlier this week.
Tehran is facing increasingly harsh warnings from U.S. President Donald Trump's administration.
U.S. Secretary of State Mike Pompeo has said that Iran's plans demonstrate the country's defiance of a UN Security Council resolution. That resolution calls on Iran to undertake no activity related to ballistic missiles capable of delivering nuclear weapons.
Iran insists the launches do not violate the resolution.
Washington and its allies worry the same satellite-launching technology could be used to develop nuclear-capable missiles.