The top U.S. military commander says there are "extraordinary and increasing concerns" about Iran's nuclear ambitions.
But Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, suggested any military action is "not the preferred path at this point."
Reuters, meanwhile, reports Western powers at the UN have circulated fresh sanctions proposals against Iran for its failure to stop enriching uranium.
At an IAEA meeting in Vienna, the United States and European Union accused Iran of violating rules by escalating uranium enrichment without UN surveillance.
Luiz Inacio Lula da Silva, the president of Brazil -- a nonpermanent member of the Security Council -- spoke in favor of more talks with Tehran, saying Iran should not be pushed "into a corner."
He spoke with U.S. Secretary of State Hillary Clinton in Brasilia to convince Brazil to back a fourth round of UN sanctions against Iran.
She said more sanctions would force Iran "to negotiate in good faith."
compiled from agency reports