"Ahmadinejad announced his agreement in principle on Brazilian President Lula Da Silva's proposal and called for continuation of talks on technical issues in Tehran," Fars said.
Details of the deal were vague, specifically whether Ahmadinejad had agreed to ship Iran's low-enriched uranium outside of the country - a key demand from several world powers.
A new position?
The so-called "P5+1 countries" - the members of the United Nations Security Council, plus Germany - have spent the last eight months trying to negotiate an international fuel swap with Iran.
Ahmadinejad has, in the past, repeatedly refused any deal that requires shipping the fuel to another country, and it is unclear whether he has changed his stance.
"Unless Iran proposes some significant concessions, the likelihood [of a deal] is low," said Gala Riani, an analyst for IHS Global Insight Middle East, in an interview with Reuters.
Brazilian officials have said in the past that they'd be willing to serve as "guarantors" for the fuel swap.
Ahmadinejad also warned that a new round of UN sanctions against Iran could permanently damage Tehran's ties with the United States.
Speaking at a news conference in New York on Tuesday, he said US-negotiated sanctions will not prevent Iran from pursuing its nuclear ambitions.
But in an interview with Al Jazeera, he also admitted that internal politics within both Iran and the US were making it difficult to reach any kind of deal on the issue.
"Sanctions cannot stop the Iranian nation. The Iranian nation is able to withstand the pressure of the United States and its allies," he said on the sidelines of the UN nuclear non-proliferation treaty (NPT) conference.
"While we do not welcome sanctions, we do not fear them either.
"The relationship between Iran and the United States will never improve again [if sanctions are approved]."
The US, Britain and France have been pressing for a fourth round of UN penalties on Iran for its refusal to halt a key part of its nuclear programme that they say could be used to make weapons.
Iran says it only wants the technology to produce nuclear energy.
'Acting too hastily'
Ahmadinejad told Al Jazeera that he and Barack Obama, the US president, would have to refrain from "acting too hastily" if the two sides are to reach agreement on the impasse.
"For example, the resolution presented to the IAEA [International Atomic Energy Agency] against Iran in the presence of Mr Obama was a very negative, hasty action that had very negative repercussions in Iran," he said.
He was referring to a November 2009 resolution adopted by the UN nuclear agency that criticised Iran for defying a UN Security Council ban on nuclear enrichment.
The resolution also rebuked Tehran for secretly building a uranium enrichment facility near the city of Qom.
"[The] resolution was not based on any legal or lawful framework but surely a political, politicised act ... It reduced public confidence in the [negotiation] process in Iran."