PARIS, Oct 13 (Reuters) - A pending visit to Tehran by the European Union coordinator for talks to revive the Iran nuclear deal cannot be deemed "business as usual" given escalating Iranian nuclear activities and the stalling of negotiations since June, European diplomats said. Enrique Mora, the EU"s political director, is due to hold talks on Thursday with members of Iran"s nuclear negotiating team four months after talks broke off between Iran and world powers, including the United States, to rescue the accord. "The visit comes at an important time," the diplomats from Britain, Germany and France, known as the E3, said in a note on Wednesday. The three countries along with China and Russia are parties to the deal. "The situation in the nuclear field has been worsening and been aggravated continuously since then," they said, alluding to Iran"s accelerating enrichment of uranium to higher fissile purity, a possible pathway to a nuclear bomb. "For this reason, we do not see this visit as "business as usual", but rather as a decisive visit in the crisis." The Islamic Republic has repeatedly said it will return to the negotiations "soon" without giving any sense of what that actually means. Western diplomats have tentatively said a return to the Vienna talks may be possible before the end of October. "Through its statements and actions on the ground, the new Iranian administration of President (Ebrahim) Raissi raises doubts about its intention to return to the Joint Comprehensive Plan of Action (JCPoA)," French Foreign Ministry spokeswoman Anne-Claire Legendre told reporters in a daily online briefing."While refusing to negotiate, Iran creates facts on the ground that further complicate the return to the JCPoA," she said, adding that Tehran would also need to be clear about its intentions should it come back to the talks. Since then-U.S. President Donald Trump ditched the deal in 2018 and reimposed sanctions on Iran, Tehran has been rebuilding stockpiles of enriched uranium, refining it to higher levels of purity and installing advanced centrifuges to speed up enrichment. President Joe Biden aims to restore the deal to restrain Iran"s nuclear programme but the sides disagree on which steps need to be taken and when. Key issues include what nuclear limits Tehran will accept, what sanctions Washington will remove, whether there will be any guarantees and the prospect of follow-on talks on Iran"s future nuclear programme, regional and ballistic missile activities, diplomats have said. Mora said on Twitter that he would raise the "urgency to resume" the talks from where they left off in June. Diplomats have said they are concerned Tehran"s new negotiating team - under a president known as an anti-Western hardliner unlike his pragmatist predecessor - may make new demands beyond the scope of what had already been agreed. Iranian Deputy Foreign Minister Ali Bagheri Kani, who is expected to lead Iran"s new negotiating team, confirmed on Wednesday that he would meet Mora. "Exchanging views on bilateral & regional issues including Afghanistan, as well as talks on removal of cruel sanctions, are on the agenda," he said.