And so some analysts think that Iran is actually eager to have substantive talks with the United States.
The agreement stops short of declaring a ceasefire, and was about trying to build trust ahead of more substantive talks, says the BBC's Jonah Fisher in Bangkok.
BBC: Burma government, Kachin rebels in deal to hold more talks
But this spring Rhodes credited the sanctions with prompting Iran to participate in multilateral talks, in Istanbul, that set the stage for more substantive talks, in Baghdad later this year.
But there was also skepticism in Washington and Brussels that Iran was committed, or capable, in the coming months to engage in substantive talks aimed at eliminating Tehran's ability to produce nuclear weapons.
WSJ: Iran Says It Is Set for Nuclear Talks, but West Is Skeptical
"This meeting tomorrow and Wednesday will be to establish a framework for substantive talks later, but we haven't got a date yet, " a spokesman for the Department of Environment, Transport and the Regions said.
But it is difficult to see how substantive talks can even get started, given the differences between the two sides over what must be done, or not be done, as a prerequisite for serious negotiation.
Substantive peace talks began last year with the backing of Turkey's government, still keen on a settlement similar to that proposed in the Annan plan.
The talks were the first substantive negotiations between the two sides since the war.
However, at the last round of talks in December, there was substantive progress on sensitive issues such as intellectual property rights, where China has a poor record.
Holbrooke said peace talks have entered an extremely serious and substantive phase.
CNN: NATO warns Bosnian Serbs: obey demands or face air strikes
Diplomatic sleights-of-hand to start talks or to preserve the settlement freeze touch on substantive issues: the borders of the two states and the political and religious demarcation of Jerusalem.
The Government of Burma has made progress towards political reform in a number of areas, including by releasing hundreds of political prisoners, pursuing ceasefire talks with several armed ethnic groups, and pursuing a substantive dialogue with the democratic opposition.
The Palestinian leader emerged from Saturday's meeting saying he hoped it would lead the way back to substantive peace negotiations, and he told CNN that he is personally ready to begin such talks immediately with the Israelis, in any format.
Both Boehner and McConnell have complained that Obama refuses to address needed spending cuts and entitlement reforms to bring about substantive deficit reduction, and the timing of the phone calls appeared in response to questions about a lack of formal talks involving the president.
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