The US government did not consider the deployment of Stuxnet as an act of war against Iran.
"It’s a covert action. And the U.S. government has, ever since the end of World War II, before then, engaged in covert action."
The Pentagon wanted to ensure that there was minimal collateral damage, as part of the Law of Armed Conflict designed to minimise civilian impact.
"It very much had the feel to it of having been written by or governed by a team of Washington lawyers."
To this day, the Government of the United States officially considers any documents regarding Stuxnet, codename Operation Olympic Games, to be classified (NOFORN TS STLW).
In the documentary Zero Days, an unknown NSA informant explained that Stuxnet was one of several attempts by the United States government to sabotage Iran's nuclear program, such as Operation Merlin and Operation Nitro Zeus.
Iran considered Stuxnet as an attempt "to sabotage the uranium enrichment facility at Natanz”.
"Iran respects international law and refrains from targeting other nations’ economic or financial institutions"
The establishment of the Iranian Cyber Defence Command was the government response - the ICDC is now the 4th biggest cyber army in the world (After the USA, Germany and Japan). However, most of the ICDC’s capacity is for defense, while APT groups such as Rocket Kitten engage in offensive actions.