The US had wanted Brazil to support UN sanctions against Iran
Brazil will not bow to pressure from the US to support further sanctions against Iran over its nuclear work, the country's foreign minister has said.
Celso Amorim told US Secretary of State Hillary Clinton that Brazil wanted to see further negotiations on the issue before it would support sanctions.
Mrs Clinton said that sanctions had to be passed first in order to persuade Iran to "negotiate in good faith".
The US fears Iran is developing nuclear weapons, a charge Tehran denies.
At a news conference with Mrs Clinton in the Brazilian capital, Brasilia, Mr Amorim said: "We will not simply bow down to an evolving consensus if we do not agree.
"We have to think by ourselves and with our values and principles," he said.
Washington wants Brazil, which enjoys good ties with Iran, to support its push for a fourth round of UN sanctions against Tehran over its refusal to stop enriching uranium - a possible step to building atomic weapons.
Tehran says the uranium is being enriched to provide fuel for nuclear power reactors it envisages building.
Brazil is currently a member of the UN Security Council.
"I think it's only after we pass sanctions in the Security Council that Iran will negotiate in good faith," Mrs Clinton said.
"The door is open for negotiations. We never slammed it shut," she said. "But we don't see anybody, even in the far-off distance, walking toward it."
Even before talks with Mrs Clinton began, Brazilian President Luiz Inacio Lula da Silva repeated his stance that isolating Iran's leaders is counter-productive.
"It is not prudent to push Iran against a wall. The prudent thing is to establish negotiations," he said.
"I want for Iran the same thing as I wish for Brazil: To use the development of nuclear energy for peaceful purposes. If Iran is in agreement with that, Iran will have Brazil's support."
President Lula said he did not want Iran to develop nuclear weapons and would raise the issue in a visit to Tehran in May.
Mrs Clinton is visiting South America at a time when there is a sense in the region that President Barack Obama's administration, distracted by so many other issues, has not lived up to expectations, says the BBC's Gary Duffy in Sao Paulo.
The US state department has said if Brazil uses its relationship with Iran to press the country to fulfil its international obligations then that would be an important step, but if it did not do that, Washington would be "disappointed".