Intercepted conversations between representatives of the Iranian and Argentine governments point to a long pattern of secret negotiations to reach a deal in which Argentina would receive oil in exchange for shielding Iranian officials from charges that they orchestrated the bombing of a Jewish community center in 1994.
The transcripts were made public by an Argentine judge on Tuesday night, as part of a 289-page criminal complaint written by Alberto Nisman, the special prosecutor investigating the attack. Mr. Nisman was found dead in his luxury apartment on Sunday, the night before he was to present his findings to Congress.
But the intercepted telephone conversations he described before his death outline an elaborate effort to reward Argentina for shipping food to Iran — and for seeking to derail the investigation into a terrorist attack in the Argentine capital that killed 85 people.
The deal never materialized, the complaint says, in part because Argentine officials failed to persuade Interpol to lift the arrest warrants against Iranian officials wanted in Argentina in connection with the attack.
The phone conversations are believed to have been intercepted by Argentine intelligence officials. If proved accurate, the transcripts would show a concerted effort by representatives of President Cristina Fernández de Kirchner’s government to shift suspicions away from Iran in order to gain access to Iranian markets and to ease Argentina’s energy troubles.
The contacts came at a time when Iran was seeking to raise its profile in Latin America. In recent years, Iran has forged close ties with leftist governments in Venezuela and Bolivia, while also turning to large commodities producers like Brazil for food imports and as a counterweight to its isolation by the West over its nuclear program.
Officials in Mrs. Kirchner’s government have lashed out at Mr. Nisman and his assertions before and after his death, saying that he had been manipulated by Antonio Stiusso, a former senior intelligence official ousted by the president in December. Aníbal Fernández, the presidential secretary, described Mr. Nisman’s complaint on Wednesday as “absolutely feeble.”
The complaint asserts that the negotiators included Argentine intelligence operatives and Mohsen Rabbani, a former Iranian cultural attaché in Argentina charged with helping to coordinate the bombing.
In one transcript from 2013, an Argentine union leader and influential supporter of Mrs. Kirchner said he was acting on the orders of the “boss woman,” adding that the government was open to sending a team from the national oil company to advance the negotiations.
“He’s very interested in exchanging what they have for grains and beef,” said the union leader, Luis D’Elía, referring to a powerful Argentine minister with whom he had just met.
Another intercept shows negotiators talking about ways to place blame for the bombing on right-wing groups and activists.
Yet another transcript includes a discussion about swapping not just Argentine grains, but weapons as well, for Iranian oil.
“The publication of Nisman’s complaint is a first step that can contribute to the transparency of an investigation plagued by mystery and frozen for 20 years in a tomb of impunity,” Fernándo González, an editor at the newspaper El Cronista, wrote on Wednesday, arguing that it would pave the way for new investigators and for Mrs. Kirchner to defend herself.
Mr. Nisman asserted for years that Iran had helped plan and finance the bombing, and that its Lebanese ally, the militant group Hezbollah, had carried it out. His body was found at his apartment on Sunday with a gunshot wound to his head in a murky episode that government officials have called a suicide. An investigation by a prosecutor is underway.
Some experts, including a former American F.B.I. agent who helped the Argentines in their investigation, have questioned the claims of direct Iranian involvement in the bombing. Still, Argentina had limited relations with Iran for years, partly because of the investigation’s importance to the nation’s large Jewish population.
Then, in 2013, Argentina announced that it had reached an agreement with Iran to establish a joint commission to investigate the attack. The move was backed by Argentina’s Congress but faced stiff resistance by some who feared that it would make an impartial investigation unlikely. An Argentine court declared the agreement unconstitutional last year, and the government pledged to appeal.
Just last week, Mr. Nisman, 51, raised tensions further by accusing top Argentine officials, including Mrs. Kirchner, of conspiring with Iran to cover up responsibility for the bombing.
He said the effort seemed to begin with a secret meeting in Aleppo, Syria, in January 2011 between Héctor Timerman, Argentina’s foreign minister, and Ali Akbar Salehi, Iran’s former foreign minister.
At the meeting, the complaint contends, Mr. Timerman informed his Iranian counterpart that Argentina was no longer interested in supporting the investigation into Iran’s possible role in the attack. Instead, Argentina initiated steps toward a détente, with an eye on improving trade between the two countries.
After this meeting, Mr. Nisman said a covert team of Argentine negotiators, including Mr. D’Elía, who has publicly asked whether Israel was to blame for the 1994 bombing, tried in vain to exchange Iran’s immunity for oil.
Mr. Nisman said the negotiators, including intelligence agents, were given the task of “constructing a false hypothesis, based on invented evidence, to incriminate new authors” of the 1994 bomb attack.
Mr. D’Elía declined to comment on Wednesday night. Mr. Timerman, the foreign minister, has rejected Mr. Nisman’s accusations, emphasizing that Argentina had not asked Interpol to lift the warrants.
Mrs. Kirchner’s cabinet chief, Jorge Capitanich, also sought to discredit the findings, saying that Argentina had not imported crude oil from Iran.
Separately, Telám, the official news agency, called the complaint a “labyrinth of inconsistencies,” contending that an operative identified by Mr. Nisman as an intelligence agent was not linked to Argentina’s intelligence secretariat. It also said that grain exports were carried out by agribusiness companies, arguing that the government could not have reached a deal without them.
While the complaint made it clear that a deal did not reach fruition, contending it fell apart because of frustrations on the Iranian side, other countries have pursued oil-for-food exchanges in the region. In the Caribbean, Hugo Chávez, then the president of Venezuela, agreed to supply oil to the Dominican Republic partly in exchange for imports of food like black beans.
But a deal with Iran would carry additional risks. A spokeswoman for the Treasury Department in Washington declined to comment on whether oil shipments from Iran to Argentina would be in violation of the sanctions enacted over Iran’s nuclear program. But on its website, the Treasury Department explains that bartering for Iranian oil could result in sanctions.
Either way, during the period in which the secret negotiations were unfolding, Iran re-emerged as an important trading partner for Argentina, at a time when the country was seeking new markets for its commodities in the Middle East and Asia.
“Trade improved significantly between Argentina and Iran since 2010 with large surpluses in Argentina’s favor, before dropping off in 2014,” said Juan Gabriel Tokatlián, an international relations expert at Torcuato di Tella University in Buenos Aires, pointing to annual trade volumes of more than $1 billion a year this decade, compared with negligible levels in the previous decade.
Beyond trade, the warming relations between Argentina and Iran extended into the diplomatic realm, according to the intercepted calls.
“We’re doing very well,” Ramón Héctor Bogado, who is identified in the complaint as an Argentine intelligence operative, said about the signing of the 2013 memorandum on a joint investigation into the bombing.
“We have to work calmly,” Mr. Bogado told a man identified in the complaint as go-between on the Iranian side. “We have a job to do for the next 10 years.”
But in just a few months, the transcripts suggested, the mood had changed as it became clear that Interpol would not lift the arrest warrants on the Iranians.
“It looks like” Argentina’s foreign minister “messed up,” the go-between for Iran is quoted as saying in the complaint after returning from Tehran in May 2013, when it was becoming clear that Interpol would not remove the warrants.
Jonathan Gilbert reported from Buenos Aires, and Simon Romero from Rio de Janeiro. Rick Gladstone contributing reporting from New York.