Iran blamed Israel for a drone attack on a military factory near the central city of Isfahan, the semi-official ISNA news agency said on Thursday, vowing revenge for what appeared to be the latest episode in a long-running covert war. The attack came amid tension between Iran and the West over Tehran's nuclear activity and its supply of arms – including long-range "suicide drones" - for Russia's war in Ukraine, as well as months of anti-government demonstrations at home. In a letter to the UN chief, Iran's UN envoy, Amir Saeid Iravani, said "primary investigation suggested Israel was responsible" for Saturday night's attack, which Tehran had said caused no casualties or serious damage. "Iran reserves its legitimate and inherent right to defend its national security and firmly respond to any threat or wrongdoing of the Zionist regime (Israel) wherever and whenever it deems necessary," Iravani said in the letter. "This action undertaken by the Zionist regime (Israel) goes against international law,” Reuters quoted him as saying. Arch-foe Israel has long said it is willing to strike Iranian targets if diplomacy fails to curb Tehran's nuclear or missile programs, but does not comment on specific incidents. Talks between Iran and world powers to revive a 2015 nuclear deal have stalled since September. Under the pact, abandoned by Washington in 2018 under then-President Donald Trump, Tehran agreed to limit nuclear work in return for easing of sanctions. Iran has accused Israel in the past of planning attacks using agents inside Iranian territory.