VIENNA - Diplomats from Iran and five world powers recommitted on Sunday to salvaging a major nuclear deal signed in 2015 amid mounting tensions between the West and Teheran since the United States withdrew from the accord and reimposed sanctions.

Representatives of Iran, Germany, France, Britain, China, Russia and the European Union met in Vienna to discuss the Joint Comprehensive Plan of Action, or JCPOA, which restricts the Iranian nuclear program.

"The atmosphere was constructive, and the discussions were good," Iran's top nuclear negotiator Abbas Araghchi told reporters after the meeting ended.

"I cannot say that we resolved everything" but all the parties are still "determined to save this deal," he added.

Fu Cong, the head of Chinese delegation, said that while there were "some tense moments" during the meeting, "on the whole the atmosphere was very good. Friendly. And it was very professional".

"I have two takeaway messages from today's meeting," said Fu, also director general of the Department of Arms Control at the Chinese Foreign Ministry, at a news conference following the meeting. "First, all sides have expressed their commitment to safeguard the JCPOA and to continue to implement the JCPOA in an objective manner, and a balanced manner."

"The second point I take away from the meeting is that all sides have expressed their strong opposition against the US unilateral imposition of sanctions, especially the extraterritorial application of the sanctions, and they also expressed support and appreciation of China's efforts to implement the JCPOA, in particular China's effort to maintain normal trade and oil relations with Iran," Fu said.

Higher-level meeting

Both Fu and Araghchi said there was a general agreement to organize a higher-level meeting of foreign ministers soon, but also that preparations for such a summit needed to be done well. A date has not been set.

Iran is pressuring the remaining parties to the deal to offset the sanctions US President Donald Trump reinstated after withdrawing last year. Iran recently surpassed the uranium stockpile and enrichment limits set out in the agreement, saying the action could be reversed if the other parties came up with economic incentives.

So far, neither Iran's announcement that it exceeded the amount of low-enriched uranium allowed under the deal nor its revelation it had begun enriching uranium past the 3.67 percent purity allowed, to 4.5 percent, are seen as violations likely to prompt the European parties to invoke a dispute resolution mechanism.

Both of Iran's actions were verified by the United Nations' nuclear watchdog, the International Atomic Energy Agency.

Iran is keen on the activation of a barter-type system set up by the Europeans that would allow the continent's businesses to trade with Teheran without violating the US sanctions.

Araghchi said the European system was "not functioning yet, but it is in its final stages".