Brazil and the US clashed Wednesday over how to rein in Tehran's suspect nuclear ambitions as Brazilian President Luiz Inacio Lula da Silva warned the world not to "push Iran into a corner."

In talks with US Secretary of State Hillary Clinton, Lula and his foreign minister Celso Amorim backed continued international negotiations to ensure Iran does not enrich uranium to the point it can build a nuclear bomb.

Lula set a tough tone for his and Amorim's talks with Clinton when he said it is "not prudent to push Iran into a corner. It is prudent to make it so that Iran continues to negotiate."

In a combative press conference with Amorim, a stern-faced Clinton retorted that the US-led drive to impose a fourth set of UN sanctions on the Islamic Republic was the only way to bring it back to the negotiating table.

"Only after we pass sanctions in the Security Council will Iran negotiate in good faith," Clinton said in a foreign ministry briefing room where she was continually pressed by local journalists on Washington's hard stand.

Clinton echoed Amorim when she said both shared the goal of preventing Iran from becoming a nuclear weapons country, but said the two differed in how to attain it.

"Once the international community speaks in unison around a resolution, then the Iranians will come and begin to negotiate," she said, raising her voice.

"So we want to get to the negotiation. We just think the best path is through the United Nations Security Council."

She also appeared to suggest Brazil and other countries were falling for what the US consider is antics by Iran.

"We see an Iran that runs to Brazil, an Iran that runs to Turkey, and an Iran that runs to China telling different things to different people to avoid sanctions," she said.

Brazil is a current voting member on the 15-strong UN Security Council, though it is not one of the five permanent veto-wielding members, which are Britain, China, France, Russia and the United States.

But China appears to stand alone among the permanent members in resisting sanctions, with Russia appearing to move toward them.

When asked why Brazil was going against the growing consensus, Amorim responded sharply, "It's not a matter of Brazil refusing to join a nuclear consensus."

Rather, he said it was a question of determining whether coercive measures like sanctions would work to achieve a consensus.

"Our view is that sanctions, in general, are counterproductive," he said, adding that Brazil believed diplomacy was "worth the effort."

"The director of the International Atomic Energy Agency will come to Brazil and I am going to suggest to him that he convene a meeting with the Iranian negotiators, perhaps with the presence of some new interlocutor," he said.

"Once the international community expresses itself, sends a clear message, by means of a UN resolution, the Iranians will negotiate. And that is why the best path is through the UN Security Council," he said.

Clinton's visit to Brazil was preceded Friday by William Burns, the US undersecretary of state for political affairs, who leads US consultations on Iran among the permanent five members of the UN Security Council plus Germany.

The so-called P5-plus-1 group has for years spearheaded efforts to halt Iran's nuclear program, which the west fears masks a drive for a nuclear weapon but which Iran says is for peaceful nuclear energy.

A senior European diplomat in Washington told reporters last week that China might abstain in a UN sanctions vote, along with Brazil, Turkey and Lebanon.

Brasilia was Clinton's fourth stop on a six-nation Latin America tour, following visits to Chile, Argentina and Uruguay.

Clinton and Amorim signed agreements to curb global warming, increase opportunities for women and promote economic development in both Latin America and Africa, US officials said.