"This is an economic war against Iran but".
But President Donald Trump announced last May that the USA would withdraw from the agreement.
In a statement, US Treasury Secretary Steven Mnuchin said, "Treasury's imposition of unprecedented financial pressure on Iran should make clear to the Iranian regime that they will face mounting financial isolation and economic stagnation until they fundamentally change their destabilising behaviour".
The US secondary sanctions have been re-imposed at the end of a 180-day wind down period which followed the announcement that the US was pulling out of the Iran deal.
Iranian President Hassan Rohani said on Iranian television Monday that his country would try to continue to sell oil to break the USA sanctions. US light crude was 15 cents lower at $62.99. "We will continue talking to the rest to bring oil imports to zero", Pompeo said.
The second wave of renewed US sanctions on OPEC's third largest exporter officially started on Monday targeting Iran's energy, shipbuilding, shipping, and financial sectors.
Milner milestone in vain as Arsenal holds Liverpool 1-1
We made, I think, more mistakes than the refs but I think in this moment it would have been cool if the goal could count. Unai Emery 's side are fourth in the table, but will move to within one point of Liverpool with three points.
News of waivers on the sanctions weighed on prices, analysts said.
Under the deal, Tehran had agreed to curb its nuclear activities in exchange for the lifting of crippling economic sanctions.
However eight countries have been granted a temporary exemption for six months despite United States warning previously that it would be harder for Iran's oil importers to get a waiver. This group takes as much as three quarters of Iran's seaborne oil exports, trade data shows, meaning Iran will still be allowed to export some oil for now.
South Korea, one of Asia's biggest buyers of Iranian oil, had asked Washington for an exemption, given that petrochemicals are key to its economy and the sanctions would exact a toll on the country's businesses.
The countries receiving waivers are China, Greece, India, Italy, Japan, South Korea, Taiwan and Turkey, and will be able to continue to purchase Iranian oil as long as they work to reduce imports to zero. The other parties to the deal - Britain, France, Germany, China and Russian Federation - say they will not leave. "But on oil, we want to go a little bit slow because I don't want to drive the oil prices in the world up", Trump told reporters at Joint Base Andrews outside Washington on Monday before leaving on a campaign trail for the mid-term polls being held on Tuesday.
The head of Iran's Central Bank, Abdolnassr Hemmati, said the country has taken necessary banking measures to continue trade after the USA move, Iranian state TV said.
"Today the enemy [the United States] is targeting our economy. the main target of sanctions is our people", Iranian President Hassan Rouhani said.