A meeting between six world powers and Iran yielded no breakthroughs Tuesday, even as leaders said they would continue to pursue diplomatic avenues and sanctions to convince Tehran to curb its nuclear program.

European Union foreign policy chief Catherine Ashton said the five UN Security Council nations and Germany, known as the P5+1, would discuss ways of breaking the impasse over Iran’s nuclear program on the sidelines of the United Nations General Assembly in New York next week, Reuters reported.

Meanwhile, Iran and the UN’s atomic watchdog, engaged in concurrent talks over access to nuclear sites, are reportedly aiming to meet next month to continue talks over the program, AFP reported, quoting diplomats close to the negotiations.

Iran, represented by chief nuclear negotiator Saeed Jalili, has thus far refused to budge in both negotiations, though world powers agree that time remains for diplomacy and sanctions to work before military action need be considered.

Ashton’s spokesman called the P5+1 talks in Istanbul Tuesday night “constructive,” saying they were ”an important opportunity to stress once again to Iran the urgent need to make progress.”

The sides have met several times since April, though little progress has been made in the effort to come to terms over curbing Iran’s enrichment activities. Israel, which has called for tough sanctions and possibly even military action to thwart Tehran, has characterized the talks as a stalling tactic.

Tehran has fallen under an increasingly heavy sanctions regime, but reports indicate that it is finding creative ways to skirt embargoes on its oil exports and on incoming equipment.

Before Tuesday’s meeting, British Foreign Secretary William Hague threatened to impose yet harsher sanctions if the talks continued to falter.

“We will be intensifying those sanctions in the coming weeks and months in the absence of successful negotiations,” he said in London, while also warning Israel off taking military action.

Hague is looking to convene a meeting of EU ministers next month to discuss further crippling Iran’s economy as a means of convincing it to abandon its nuclear program, according to Reuters.

On Tuesday night, the news agency reported that Bahrain and the United Arab Emirates, both regional rivals of Iran, had confiscated items headed for Iran that could be used for the manufacture of nuclear weapons and reported the incident to the United Nations Security Council.

Iran says its nuclear program is peaceful, though Israel and many Western powers dispute the claims. On Sunday, Prime Minister Benjamin Netanyahu, who has reportedly agitated for a military strike — or at least the credible threat of such action — said the Islamic Republic was nearly 90% of the way toward building a nuclear bomb.

The International Atomic Energy Agency — which has so far failed to gain access to the Parchin nuclear site, where it believes traces of nuclear tests have been found — called Tuesday for Iran to cooperate with inspectors.

The move came a day after Iran lashed out at the agency, accusing it of harboring terrorists looking to undermine the Islamic Republic.