Tehran, Tehran Province, Iran
Iran's supreme leader Ayatollah Ali Khamenei on Wednesday called the end of oil sanction waivers by the United States a "hostile measure" that "won't be left without a response".
"US efforts to boycott the sale of Iran's oil won't get them anywhere. We will export our oil as much as we need and we intend," his official English-language Twitter account said.
"They (the US) wishfully think they have blocked Iran oil sales, but our vigorous nation and vigilant officials, if they work hard, will open many blockades," Khamenei said on Twitter.
"Enemies have repeatedly, in vain, taken action against our great nation, revolution... but they must know Iranians won't give in," he added.
The United States on Monday demanded that buyers of Iranian oil stop purchases by May 1 or face sanctions, ending six months of waivers which allowed Iran's eight biggest buyers, most of them in Asia, to continue importing limited volumes.
Before the reimposition of sanctions last year, Iran was the fourth-largest producer among the Organisation of the Petroleum Exporting Countries at around 3 million barrels per day (bpd), but April exports have shrunk to below 1 million bpd, according to tanker data and industry sources.
US President Donald Trump has been clear to his national security team over the last few weeks that he wants the waivers to end, and national security adviser John Bolton has been working the issue within the administration.
The US reimposed sanctions in November on exports of Iranian oil after Trump unilaterally pulled out of a 2015 nuclear accord between Iran and six world powers. Washington is pressuring Iran to curtail its nuclear program and stop backing militant proxies across the Middle East.
Along with sanctions, Washington has also granted waivers to eight economies that had reduced their purchases of Iranian oil, allowing them to continue buying it without incurring sanctions for six more months. They were China, India, Japan, South Korea, Taiwan, Turkey, Italy and Greece.