Iranian media say the country's gas stations have been the target of a cyberattack that left many motorists stuck in long lines at closed stations.
The attack, which was reported by the semiofficial ISNA news agency, targeted a government system that manages fuel subsidies.
The Associated Press reports its journalists saw long lines at stations in the country's capital, Tehran.
"I have been waiting a couple of hours for the gas stations to reopen so that I can fill up," said a motorcyclist who gave his name only as Farzin, AP reported. "There is no fuel wherever I go."
ISNA said that when people tried to buy fuel with government subsidy cards, they received the message, "Cyberattack 64411."
That number was also seen during a summer cyberattack on the country's railway system.
Most Iranians rely on the subsidy cards, which allow them to buy gas at extremely low prices compared to much of the rest of the world.
Iranian state TV reported that officials were holding an emergency meeting to address the apparent hack.
Some Persian-language news outlets based outside Iran reportedly showed videos shot in the city of Isfahan showing an electronic billboard reading, "Khamenei! Where is our gas?"
Ayatollah Ali Khamenei is Iran's supreme leader.
The attack came on the birthday of the late Shah of Iran, Mohammad Reza Pahlavi, who fled the country in 1979 in the face of the Islamic Revolution, also known as the Iranian Revolution.
It also comes near the anniversary of the November 2019 rise in fuel prices, which set off large-scale protests. Hundreds were reportedly killed when the government cracked down on the protesters.
Some information in this report comes from The Associated Press and Reuters.