"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 and two other permanent members of the UN Security Council 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 could be used to make weapons.
Iran says it only wants the technology to produce nuclear power.
'Acting too hastily'
Ahmadinejad told Al Jazeera on Tuesday 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."
The measures against Iran come as part of pressure on Obama to serve interest groups with respect to Tehran's nuclear programme, Hooman Majd, an Iranian-American writer, said.
"I think a lot of Iranians would agree [with Ahmadinejad] - even on the reform side - that the US and Barack Obama, in particular, is under tremendous pressure by various interest groups to not deal with Iran or to deal with Iran differently," he told Al Jazeera.
He said there were those telling the president "not to negotiate because negotiation is fruitless in the minds of many - right-wing Americans, neocons and the Israeli lobby. There is all kinds of different areas where Obama has to be very careful".
Al Jazeera's Kristen Saloomey, reporting from the UN, said other countries also appear to sympathise with Iran.
"We've seen sympathies for comments from Mahmoud Ahmadinejad from countries who themselves are pursuing nuclear technology for peaceful purposes and want to develop their nuclear reactors," she said.
Also on Tuesday, UN Security Council powers met to discuss ways to punish Tehran, as a final document detailing ways to achieve goals of checking the spread of nuclear weapons was being drafted.
US officials have said they would be looking to isolate Iran and to produce an unofficial document calling for stricter enforcement of the NPT, which requires signatories to abandon nuclear weapons.
The document could be signed by the overwhelming majority of signatory countries, but because it requires a consensus of all parties - including Iran - it would be highly unlikely to censure Tehran and could block consensus, analysts said.
Our correspondent said that the "document ... calls on Israel to sign up and join the NPT. Israel is widely believed to have nuclear weapons but has not confirmed or denied their existence".
"By signing up to the NPT, they would be required to do that. Of course, other countries as well are being asked to do that - India and Pakistan are also nuclear states who have not joined the NPT," she said.
The NPT is formally reviewed every five years at a meeting of all 189 treaty members - all the world's nations except India, Pakistan, Israel and North Korea, all of which either have confirmed or are believed to have nuclear weapons.