Nuclear talks between Iran and six world powers have been described as showing signs of promise after previous discussions screeched to a halt nearly 15 months ago.
Iran is sitting down with the United States, Britain, China, France, Germany and Russia to discuss Tehran's contentious atomic program.
Iran is facing four sets of UN sanctions for its refusal to stop enriching uranium, an activity that the United States and other countries fear is for the purposes of producing nuclear weapons.
Iran has long asserted that the program is innocuous.
Though diplomats have painted the talks as being positive, tension between Iran and the United States was palpable Saturday afternoon, as an Iranian official said the country had refused a proposal from Washington for a one-on-one meeting.
"No bilateral talks with the U.S. will be formed," Alaeddin Boroujeddi, head of Iran's powerful parliamentary committee on national security and foreign policy, told The Associated Press. "It is not Iran's policy to have bilateral talks with the U.S. -- Iran will talk to them on the multilateral level."
Relations have been strained between the two countries for more than 30 decades, since militant Iranian students took American diplomats hostage in Iran.
Going into discussions, diplomats say expectations were low, with the negotiators hoping to get Iran to simply talk about the enrichment program.
An anonymous diplomat told AP that Iran appeared to be open to that objective, willing to participate in talks about the peaceful use of nuclear energy. The person asked not to be named because the information he was sharing came up in a closed meeting.
"I would say there was a very constructive atmosphere compared to last time ... generally a positive vibe," he said.
Supreme Leader Ayatollah Ali Khamenei's prohibition of nuclear weapons for Iran had also been brought up, he said.
As far as goals go, many in the international community have been outspoken about their desire to convince Iran to stop all uranium enrichment in order to alleviate fears about possible weapons development.
Another anonymous diplomat, however, told AP that many influential Western nations are now of the belief that Iran should be permitted some enrichment activity "under the right circumstances." Those conditions would have to include an overall confidence that Iran wasn't using its atomic program for weapons-related purposes.
Before the weekend talks began, European Union Foreign Policy Chief Catherine Ashton expressed hope that the discussions would be "the beginnings of a sustained process."
With files from The Associated Press
