Iran on Monday accused the United States of "procrastinating" in indirect talks aimed at reinstating Tehran's 2015 nuclear deal, and said a prisoner swap with Washington was not linked to the negotiations.

After 16 months of fitful, indirect U.S.-Iranian talks, with European Union officials shuttling between the sides, a senior EU official said on August 8 it had laid down a "final" offer and expected a response within a "very, very few weeks."

Iran last week responded to the EU's text with "additional views and considerations," while calling on Washington to show flexibility to resolve three remaining issues. The United States last week said it was studying Iran's response.

"The Americans are procrastinating and there is inaction from the European sides... America and Europe need an agreement more than Iran," Iran's Foreign Ministry spokesperson Nasser Kanaani told a news conference.

Kanaani said Tehran wanted a sustainable deal that would preserve Tehran's legitimate rights.

"Until we agree on all issues, we cannot say that we have reached a complete agreement," he said.

Meanwhile, the United States has repeatedly called on Tehran to release several Iranian-Americans held in Iran on security charges. Iran has demanded several Iranians detained on charges linked to U.S. sanctions to be freed.

"We emphasize that the exchange of prisoners with Washington is a separate issue and it has nothing to do with the process of negotiations to revive the 2015 pact," Kanaani said, adding that Tehran was ready to swap prisoners.

Iran signed the nuclear deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), with world powers in July 2015, agreeing to curb its nuclear program in return for the removal of sanctions on the country. However, in 2018, former U.S. President Donald Trump pulled Washington out of the agreement and reimposed unilateral sanctions on Tehran, prompting the latter to drop some of its commitments under the pact.

"We seek a good agreement which would guarantee Iran's national interests and would be long-lasting... We won't be bitten twice," Kanaani said.

The latest round of the talks to revive the JCPOA was held in Vienna in early August after a five-month hiatus. The 2015 agreement appeared on the verge of revival in March after 11 months of indirect talks between Tehran and U.S. President Joe Biden's administration in the Austrian capital.

But talks broke down over obstacles such as Tehran's demand that Washington provide guarantees that no U.S. president would abandon the deal as Trump did.

However, the Biden administration cannot provide such ironclad assurances because the deal is a political understanding rather than a legally binding treaty.

(Cover: The flags of Iran and the U.S. are seen printed on paper. /Reuters)

(With input from Reuters)