Iran remains ready to return to nuclear talks “very soon” but the Biden administration has sent a “negative sign" by failing to lift economic sanctions and imposing new sanctions against Tehran, Iran’s new foreign minister told NBC News.

The foreign minister, Hossein Amir Abdollahian, told NBC News’ Andrea Mitchell that President Joe Biden needed to back up his talk of diplomacy with concrete actions to show Iran that Washington is serious about restoring a 2015 nuclear deal.

“They say, ‘We are ready to return to the fulfillment of our commitments.’ However, there is no action taken in order to show and prove the true will to the new Iranian administration, to the Iranian nation. And worse than that, simultaneously, they have managed to put on new sanctions,” Abdollahian said.

Abdollahian was named top diplomat by Iran’s new president, Ebrahim Raisi, a cleric elected in June.

The foreign minister, echoing previous statements from the new Iranian government, stopped short of saying exactly when Iran would be ready to return to talks with world powers to revive the 2015 nuclear agreement. The talks aimed at restoring the deal, known as the Joint Comprehensive Plan of Action (JCPOA), have been stalled since June, when Iran held its presidential election. The new government under President Raisi has said it has been assessing the results of previous negotiations.

Abdollahian said it was up to the United States to demonstrate it was serious about returning to the accord after former President Donald Trump withdrew the U.S. from the deal three years ago.

“The volume of the file of sanctions that Trump built against Iran is being carried carefully by Biden.”

“In other words, President Biden was and is criticizing the behavior of his predecessor, Mr. Trump vis-à-vis Iran, but at the same time, the volume of the file of sanctions that Mr. Trump built against Iran is being carried carefully by Mr. Biden,” he said.

If the United States was serious about pursuing negotiations, then why was it “piling up” actions, the foreign minister asked.

“This is a negative sign, signal to Iran,” he said.

The foreign minister said “the reality of the matter is that for years, we have not obtained any benefits from the JCPOA.” But the new Iranian government is now evaluating the talks undertaken by the previous Iranian administration, he said.

He said that “we are assessing and I can tell you that we have had many meetings and we will keep the window of diplomacy and negotiations open. And we will very soon return to the negotiations.”

Since Raisi entered office last month, he and his deputies have signaled a tougher line on restoring the 2015 nuclear agreement, raising the possibility that no deal will be reached between Tehran and Washington any time soon.

Before Raisi’s election in June, U.S. and Iranian negotiators appeared close to clinching a deal after six rounds of talks. The two sides had outlined an accord that would see both governments return to the 2015 nuclear agreement.

But the new president and his team appear to be in no rush to restart the negotiations, even though U.S. sanctions continue to inflict damage on Iran’s economy.

The 2015 deal, also signed by the UK, China, France, Germany and Russia, limited Iran's nuclear program in return for terminating U.S. economic sanctions. In 2018, President Trump withdrew the U.S. from the agreement, reimposed sanctions on Iran and introduced more sanctions as part of what he said was a "maximum pressure" campaign.

Abdollahian said Iran had held “constructive talks” this week with German and British officials on the nuclear issue and planned to meet with French officials on Friday.

Asked about Americans imprisoned in Iran, he said Iran was open to an exchange of American and Iranian prisoners held in each country.

“We see a prisoner swap and its potential as a purely humanitarian issue,” he said.

The foreign minister, addressing a series of assassinations of nuclear scientists and other suspected acts of sabotage that Tehran has blamed on Israel, said Iran was prepared to retaliate as needed to any attack on its national security.

“If we obtain reliable proof beyond dispute, we will respond in kind, swiftly, and without any equivocation,” he said.

Commenting on the killing of top Iranian general Qassem Soleimani in a U.S. drone strike in January 2020, he said Iran did not consider the case closed.

“From our viewpoint," he said, "the file so to speak will not be closed. Those who were the perpetrators and carried out that act of terrorism against a national hero and the champion of Iran in the fight against terrorism must be brought to justice.”