GENEVA — Iran and the European Union's chief negotiators agreed Saturday to resume talks on suspending uranium enrichment in two weeks, after Tehran ruled out freezing its program in talks that included the United States for the first time.

EU envoy Javier Solana told reporters after the Geneva talks with Iranian negotiator Saeed Jalili that the two would speak either by telephone or personally.

"The meeting was constructive, but we didn't get still the answer we were looking for," Solana said.

Jalili asked that Western powers not turn away from negotiations.

"Iran is calling on the Western powers to resume the dialogue," he said.

U.S. Undersecretary of State William Burns was also present, but did not speak publicly.

Washington's participation had raised expectations of possible compromise on a formula under which Iran would agree to stop expanding its enrichment activities. In exchange, six powers — the five permanent U.N. Security Council members and Germany — would hold off on passing new U.N. sanctions against the Islamic Republic.

But less then an hour after the talks started, Keyvan Imani, a member of the Iranian delegation, indicated that Iran was not prepared to budge on enrichment.

"Suspension — there is no chance for that," he told reporters gathered in the courtyard of Geneva's ornate City Hall, the venue of the negotiations.

There also appeared to be little progress inside the talks.

A Western diplomat in Geneva familiar with their substance said the Iranians were focusing on "the second or third step" of substantial negotiations without addressing what the six powers say is a prerequisite for such talks to happen — a freeze of their enrichment program. The diplomat demanded anonymity because his information was confidential.

The presence of Burns at the talks — the first instance of the Americans attending such meetings — had led to hopes of compromise.

The enrichment issue is key because the activity can produce either fuel for nuclear power stations or the material used in the fissile core of warheads. Iran has defied three sets of U.N. sanctions demanding it cease its program, saying it has a right to its peaceful uses under the Nuclear Nonproliferation Treaty. But there is growing concern the Islamic Republic might want to build nuclear weapons instead.

Recent Iranian statements suggest Tehran is looking to improve ties with the United States, with officials speaking positively of deliberations by the U.S. administration to open an interests section — an informal diplomatic presence — in Tehran after closing its embassy decades ago.

Iran and the United States broke off diplomatic relations after the 1979 Islamic Revolution and hostage crisis at the U.S. Embassy in Tehran. Official contacts between the two countries are extremely rare.

Imani said Iran had not yet received a proposal from the U.S. on opening a representation but would "study it positively" if it did.