The United States and the other permanent members of the U.N. Security Council said Thursday they were pleased by a new tone and attitude from Iran in talks aimed at resolving the impasse over its nuclear program and set a new round of negotiations for next month.

After a group meeting and then a one-on-one session between Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif, Kerry called the talks “constructive” and said he was struck by a “very different tone” from Iran. But he stressed that words must be translated into action if Iran wants to prove it is not seeking to develop a nuclear weapon.

“We’ve agreed to try to continue a process that would try to make concrete and find a way to answer the questions that people have about Iran’s nuclear program,” Kerry told reporters. “Needless to say, one meeting and a change in tone, that was welcome, does not answer those questions.”

“All of us were pleased that the foreign minister came today and that he did put some possibilities on the table.”

The meeting between Zarif and Kerry, who sat next to each other at a U-shaped table, was the highest-level direct contact between the United States and Iran in six years. EU foreign policy chief Catherine Ashton suggested that the two men had shaken hands and been cordial with each other.

Speaking after Kerry, Zarif said the meetings had been “very constructive” and “very businesslike.”

“We hope to be able to make progress to solve this issue in a timely fashion (and) to make sure (there is) no concern that Iran’s program is anything but peaceful,” he said.

“I am satisfied with this first step,” Zarif said. “Now we have to see whether we can match our positive words with serious deeds so we can move forward.”

He said the end result would have to include “a total lifting” of the international sanctions that have devastated Iran’s economy.

Ashton called the meeting “substantial” and announced that the parties had agreed to “go forward with an ambitious timeframe.” The next step will be a meeting of senior negotiators in Geneva on Oct 15-16, she said.

British Foreign Secretary William Hague said there had been a “big improvement in the tone and spirit” from Iran compared with representatives of the previous Iranian government.

German Foreign Minister Guido Westerwelle said the meeting had taken place in a “completely different tone, atmosphere and spirit” that what the group was used to and that a “window of opportunity has opened” for a peaceful resolution of the situation. He warned, though, that Iran’s words would have to be matched by actions.

“Words are not enough,” he said. “Actions and tangible results are what counts. The devil is in the detail, so it is now important that we have substantial and serious negotiations very soon.”

Iranian President Hassan Rouhani and Zarif, both in New York this week to attend the U.N. General Assembly, have said they are eager to clinch an agreement quickly that could bring their country relief from punishing international sanctions.

But the U.S. insists Rouhani must back up his calls for moderation with actions that verify Iran is not seeking to develop a nuclear weapon.

Encouraged by signs that Rouhani will adopt a more moderate stance than his predecessor Mahmoud Ahmadinejad, but skeptical that the country’s all-powerful supreme leader will allow a change in course, President Barack Obama has directed Kerry to lead a new outreach and explore possibilities for resolving the long-standing dispute.

Rouhani’s pronouncements at the U.N. have raised guarded hopes that progress might be possible. But they have also served as a reminder that the path to that progress will not be quick or easy.