Iran on Thursday formally blamed Israel for a drone attack that targeted a military workshop in its central city of Isfahan over the weekend, warning it “reserves its legitimate and inherent right” to retaliate.

Iran’s mission to the United Nations, in a letter it published on its website, attributed the attack late Saturday to Israel.

“Early investigations suggest that the Israeli regime was responsible for this attempted act of aggression,” the letter signed by Iranian ambassador Amir Saeid Iravani said.

Israeli officials declined to comment. However, Israel has carried out a series of attacks targeting Iran’s nuclear program and other sites since the collapse of its 2015 nuclear deal with world powers.

Details on the Isfahan attack, which happened around 11:30 p.m. Saturday, still remain scarce days after the assault. A Defense Ministry statement described three drones being launched at the facility, with two of them successfully shot down. A third apparently made it through to strike the building, causing “minor damage” to its roof and wounding no one, the ministry said.

The state-run IRNA news agency later described the drones as “quadcopters equipped with bomblets.” Quadcopters, which get their name from having four rotors, typically operate from short ranges by remote control. Iranian state television later aired footage of debris from the drones, which resembled commercially available quadcopters.

It remains unclear what the workshop produced.

Iravani’s letter to U.N. Secretary-General Antonio Guterres and the Security Council warned Tehran could respond to the attack.

“The Islamic Republic of Iran reserves its legitimate and inherent right…to defend its national security and respond resolutely to any threats or wrongful actions by the Israeli regime, wherever and whenever deemed necessary,” the letter read.

(AP)