The United States had a plan for an extensive cyberattack on Iran in case diplomatic attempts to curtail its nuclear program failed, The New York Times reported on Tuesday, citing a forthcoming documentary and military and intelligence officials.

Code-named Nitro Zeus, the plan was aimed at crippling Iran's air defenses, communications systems and key parts of its electrical power grid, but was put on hold after a nuclear deal was reached last year, it said.

The plan developed by the Pentagon was intended to assure US President Barack Obama that he had alternatives to war if Iran moved against the United States or its regional allies, and at one point involved thousands of US military and intelligence personnel, the report said.

It called for spending tens of millions of dollars and putting electronic devices in Iran's computer networks, it said.

US intelligence agencies at the same time developed a separate plan for a covert cyberattack to disable Iran's Fordo nuclear enrichment site inside a mountain near the city of Qom, the report said.

The existence of Nitro Zeus was revealed during reporting on a documentary film called Zero Days to be shown on Wednesday at the Berlin Film Festival, the Times said.

The film describes rising tensions between Iran and the West in the years before the nuclear agreement, the discovery of the Stuxnet cyberattack on the Natanz uranium enrichment plant, and debates in the Pentagon over the use of such tactics, the paper reported.

The Times said it conducted separate interviews to confirm the outlines of the program, but that the White House, the Department of Defense and the Office of the Director of National Intelligence all declined to comment, saying that they do not discuss planning for military contingencies.