"The most dangerous crisis we are going to face potentially in the next three to 10 years is if the Iranians get on the edge of developing a nuclear weapon," Obama's senior foreign policy adviser Anthony Lake said in an interview published Monday.
"If I were the Europeans I would much rather put on the table more sanctions, together with bigger carrots, and have that negotiation than I would face that crisis down the road," he added, suggesting Obama's tack should he be elected in November.
European Union nations last week agreed new sanctions over Tehran's nuclear programme, notably banning the country's largest bank, Bank Melli, from operating in Europe.
Existing UN sanctions against Tehran aim to force it to halt uranium enrichment over fears the process could be used to make a nuclear weapon.
Obama has come under fire during his campaign for saying that if elected president he is willing to hold unconditional talks with Iran, which is on a US list of state sponsors of terrorism. His Republican rival John McCain says Obama's proposal is a sign of his inexperience.
"Unless you assume that (Iranian negotiators) have IQs less than those of eggplants, they are not likely to make major concessions for the privilege of speaking with us. So the question is: what is your strategy for the talks?" Lake told the Financial Times.
"Do you believe that simply sanctioning them can drive them into concessions before you talk, or do you believe that you need to have the sanctions there as a stick at the heart of negotiations?" he added.
Iran and the United States have not had diplomatic relations since 1980 after Islamist students stormed the US mission in Tehran holding diplomats hostage for more than a year.
Washington accuses Iran of seeking nuclear weapon, a charge vehemently denied by Tehran which says its atomic programme is solely intended for generating electricity for its fast-growing population.
In early June Obama told a powerful pro-Israel lobby in Washington that he was willing to hold talks with Tehran, though only after careful preparation.
"As president of the United States, I would be willing to lead tough and principled diplomacy with the appropriate Iranian leader at a time and place of my choosing," Obama said.
But he also said he would never foreswear the military option to defend the United States or Israel from Iranian aggression.
"Its president denies the Holocaust and threatens to wipe Israel off the map. The danger from Iran is grave, it is real, and my goal will be to eliminate this threat."
