The Trump administration on Tuesday reimposed sanctions on Iran that were lifted as part of a nuclear agreement with the country - a follow-through on the order President TrumpDonald John TrumpFive takeaways from Ohio's too-close-to-call special election Mar-a-Lago insiders provided input on VA policy, personnel decisions: report Trump claims victory as Balderson holds on to slim lead in Ohio MORE gave when he withdrew from the nuclear pact in May.
"With regard to our situation do not be anxious at all".
During his meeting with North Korean Foreign Minister Ri Yong-ho in Tehran on Wednesday, Rouhani warned him that U.S. was "an unreliable and untrustworthy" negotiating partner that did not honour "any of its commitments".
The first period started Tuesday and marked the reinstatement of sanctions on the purchase of USA bank notes by the Iranian government, Iran's gold trade and other financial and industrial transactions.
"Today, America is identified as an unreliable and untrustworthy country in the world which does not adhere to any of its obligations", Rouhani said.
The US has recently impose crippling sanctions on both countries in respect of their nuclear programmes.
Trump tweeted on Tuesday that the new sanctions, which were lifted under a 2015 worldwide nuclear deal, were the most biting sanctions ever imposed.
"We are in solidarity with the European Union position, obviously we are closely monitoring this and we are doing everything possible on the diplomatic level to stimulate a direct dialogue between the United States and Iran, and we think that dialogue should always prevail", he said.
President Trump pulled out of the nuclear deal in May, calling it "disaster". But that has proved hard: European companies have quit Iran, arguing that they can not risk their USA business.
Among large European companies that have suspended plans to invest in Iran are France's oil major Total and its big carmakers, PSA and Renault.
Turkey, however, said it would continue to buy natural gas from Iran.
The United States will not be able to prevent Iran from exporting oil, Iranian Foreign Minister Mohammad Javad Zarif was cited as saying by an Iranian newspaper on Wednesday.
"NEVER, EVER THREATEN THE UNITED STATES AGAIN OR YOU WILL SUFFER CONSEQUENCES THE LIKES OF WHICH FEW THROUGHOUT HISTORY HAVE EVER SUFFERED BEFORE", Trump wrote.
Few American companies do much business in Iran so the impact of sanctions mainly stems from Washington's ability to block European and Asian firms from trading there.
Trump said Monday that he was open to new talks to reach a "more comprehensive deal" with Iran.
In a speech hours before the sanctions were due to take effect on Tuesday, Rouhani rejected negotiations as long as Washington was no longer complying with the deal.