Many of these companies initially were targeted by sanctions under President Barack Obama, but the restrictions were subsequently lifted when the US struck a deal with Iran in 2015 over its nuclear ambitions.
Secretary of State Mike Pompeo, speaking to "Face the Nation" on Sunday, described the measures as the "toughest ever" sanctions on Iran. The 28-nation European Union reportedly is preparing a new financial mechanism to help its companies avoid USA sanctions, and that could help keep Iranian oil exports flowing. "We have the knowledge and the capability to manage the country's economic affairs", Foreign Ministry spokesman Bahram Qasemi told state TV on Friday.
"We believe that China's normal cooperation (with Iran) within global law is legal and legitimate, and this shall be respected".
In May, President Donald Trump announced that the U.S. would withdraw from the agreement.
On the supply-side, oil is in ample availability despite the sanctions against Iran as output from the world's top-three producers, Russian Federation the United States and Saudi Arabia, is rising.
However eight countries have been granted a temporary exemption for six months despite USA warning previously that it would be harder for Iran's oil importers to get a waiver. Oil prices rallied above $85 per barrel in October on fears of a steep decline in Iranian exports.More news: Kawhi Leonard Lakers decision, LeBron James revelation, Luke Walton sack update
In addition to hitting Iran's energy sector, Monday's sanctions will target Iran's shipping, shipbuilding and financial sectors. Other parties to the deal, including Britain, France, Germany, China and Russian Federation, have said they will not leave the deal.
The Trump administration on Monday reimposed the last set of sanctions lifted under the Iran nuclear deal.
In Jerusalem, Israeli Prime Minister Benjamin Netanyahu hailed what he called Trump's courageous decision in reimposing the sanctions on Iran, an arch-foe of Israel.
As a result of pre-sanctions pressure by Washington, Iran's oil exports in November may not exceed 1 million to 1.5 million barrels per day (bpd), according to industry estimates, making them as little as a third of a mid-2018 peak.
British Prime Minister Theresa May's Downing Street office said Tuesday that the United Kingdom will continue to expand trade relations despite the decision. The previous tranche, in August, targeted Iranian currency transactions, its automotive sector and its trade in gold, aluminum, steel and other metals.
Late last week, US government officials signaled that the United States would be granting waivers to eight countries to continue temporarily buying Iranian oil, on the condition that they had significantly reduced purchases from Iran. Japan and South Korea have nearly reduced to zero imports.
Although imports of oil were temporarily allowed under the waiver, Korea still can not trade with Iran in any other business area such as automobiles, finance, shipbuilding, energy or minerals.