Iran has mobilised all its resources to sell oil in a "grey market", bypassing US 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 mobilised all of the country's resources and are selling oil in the 'grey 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."
'Resist and unite'
On Saturday, Iranian President Hassan Rouhani called for the country to "resist and unite" against US pressure in what he called a "war on hope" waged against the Islamic republic.
Rouhani has vowed that Iran will continue to supply oil to its major customers despite the unilateral measures adopted by the US.
Iran's economy has been battered since sanctions returned. Inflation has shot up, its currency has plummeted and imports are now vastly more expensive.
Upping the ante, the White House announced last week it would end oil purchase waivers granted to Iran's main customers –– including China, India and Turkey –– cutting Iran's access to its main source of foreign currency revenue.