WASHINGTON (Reuters) — The United States carried out a secret cyber operation against Iran in the wake of the September 14 attacks on Saudi Arabia’s oil facilities, which Washington and Riyadh blame on Tehran, two U.S. officials have told Reuters.

The officials, who spoke on condition of anonymity, said the operation took place in late September and took aim at Tehran’s ability to spread “propaganda”. One of the officials said the strike affected physical hardware, but did not provide further details.

Asked about Reuters reporting on Wednesday, Iran’s Minister of Communications and Information Technology Mohammad Javad Azari-Jahromi said: “They must have dreamt it”, Fars news agency reported.

The U.S. strike appears more limited than other such operations against Iran this year after the downing of an American drone in June and an alleged attack by Iran’s Revolutionary Guards on oil tankers in the Persian Gulf in May.

The Pentagon declined to comment about the cyber strike. “As a matter of policy and for operational security, we do not discuss cyberspace operations, intelligence, or planning”, said Pentagon spokeswoman Elissa Smith.