Iranian President Hassan Rouhani has criticised the US for new sanctions, saying they are "not compatible" with the spirit of current negotiations.
Speaking on Iranian TV, he said Iran was still committed to continuing nuclear talks with the US and five other international powers.
New sanctions on 25 firms and individuals were announced in Washington on Friday.
World powers suspect Iran seeks atomic weapons, a claim it strongly denies.
The country insists that it is enriching uranium for use in nuclear power stations and for medical purposes.
The new sanctions target those suspected of evading previous sanctions, aiding the nuclear programme or supporting terrorism, US officials said.
Speaking at a news conference broadcast on state TV, Mr Rouhani said the introduction of new sanctions was "a very ugly move" that would deepen distrust between the two sides.
"They are in conflict with the spirit of talks. They are unconstructive in my opinion," he said
However Mr Rouhani confirmed that Iran would continue nuclear talks with the P5+1 countries for a final agreement on its nuclear programme.
"If there are no excessive demands in the issue and if the opposite side shows loyalty...we can achieve a final deal," he said.
And he added: "Of course we bypass sanctions. We are proud that we bypass sanctions because the sanctions are illegal."
Talks aimed at curbing Iran's nuclear programme in exchange for ending sanctions began in February, but Iran and the six countries involved failed to reach a deal by the July 20 deadline.
Britain, China, France, Germany, Russia and the United States make up the P5+1.
Iran and the P5+1 have agreed to extend negotiations until 24 November.