Western nations offering a package of incentives to Iran in exchange for freezing its nuclear activities didn't get the answer they were looking for Saturday, and an unnamed participant in the session said the United States indicated it will seek more punitive United Nations sanctions against Iran in September, The New York Times reported Sunday.

The presence of U.S. Undersecretary of State William Burns at the meeting marked a change in American foreign policy. It was one of the highest-level diplomatic contacts between the United States and Iran in 30 years, but didn't produce any concessions from Iran on halting its uranium enrichment activities.

European Union foreign policy chief Javier Solana told reporters, "We still didn't get the answer we were looking for," adding the Iranians will have two weeks to formally respond to the Western proposal before it is taken off the table.