(Reuters) -Diplomats from Iran and the three European parties remaining in a moribund 2015 nuclear deal met in Istanbul on Friday, Iranian and British officials said, their first round of talks since the U.S. began nuclear talks with Tehran in April.

The talks between senior diplomats from Iran and Britain, France and Germany - known as the E3 - took place as U.S. President Donald Trump pushes for a deal to limit Iran's nuclear programme. On Friday he called on Iran to move quickly after he said his administration had put forward a proposal to Iran.

Iran has said it has not received such a proposal yet.

The European powers are not part of current negotiations between Iran and the United States, the fourth round of which ended in Oman on Sunday. A new round has not been scheduled yet.

However, they have held repeated talks with the Iranians most recently in March where they discussed how they saw the parameters of a deal to replace the 2015 accord.

The three powers have sought to coordinate with Washington notably on whether and when they should reimpose U.N. sanctions against Tehran - known in diplomatic circles as the "snapback mechanism" - if no agreement is reached.

That coordination has not been easy with European diplomats bemoaning a lack of clarity in U.S. policy on its negotiations with Tehran.

Iran and the Europeans agreed to hold further talks if needed, Iran's deputy foreign minister Kazem Gharibabadi said on X on Friday.

"Iran and the three European countries are determined to maintain and make optimal use of diplomacy," Gharibabadi said. "We will meet again to continue the discussions if necessary."

British diplomat Christian Turner said on X that Iran and the E3 shared a commitment to dialogue and that they agreed to meet again, without giving a timeframe.

Under the terms of a U.N. resolution ratifying the 2015 nuclear pact, the three European powers have until October 18 to trigger the snapback mechanism before the resolution expires.

According to diplomats and a document seen by Reuters, the E3 countries may do this by August if no substantial deal can be found by then.

Relations between the E3 and Iran have worsened over the last year despite sporadic meetings, against a backdrop of new sanctions imposed on Tehran over its ballistic missile programme, its detention of foreign citizens and support for Russia in its war against Ukraine.

U.S. Secretary of State Marco Rubio met the equivalent of national security advisers of the E3 powers also in Istanbul on Friday to discuss Iran and Ukraine, a U.S. official said.

(Additional reporting by John Irish and Humeyra Pamuk; [email protected]; Editing by Ros Russell)