Iran has mobilized all its resources to sell oil in a "gray market," bypassing U.S. sanctions that Tehran sees as illegitimate, state media quoted Deputy Oil Minister Amir Hossein Zamaninia as saying on Sunday.

The United States told buyers of Iranian oil to stop purchases by May 1 or face sanctions, ending six months of waivers that had allowed Iran's biggest customers to import limited volumes.

"We have mobilized all of the country's resources and are selling oil in the 'gray market'," Zamaninia was quoted by state news agency IRNA as saying. "This is not smuggling. This is countering sanctions which we do not see as just or legitimate."