VIENNA, Dec 13 (Reuters) - Major powers and Iran have yet to get down to business at talks on rescuing the 2015 nuclear deal, which will very soon become "an empty shell" without progress, senior British, French and German diplomats said on Monday. "As of this moment, we still have not been able to get down to real negotiations," the diplomats from the so-called E3 said in a statement about the Vienna nuclear negotiations in which they are shuttling between U.S. and Iranian officials. "Time is running out. Without swift progress, in light of Iran"s fast-forwarding of its nuclear programme, the JCPOA will very soon become an empty shell," they added, referring to the deal, whose full name is the Joint Comprehensive Plan of Action. The statement offered a pessimistic assessment of efforts to revive the deal under which Iran had limited its nuclear program in return for relief from U.S., European Union and U.N. economic sanctions. Republican then-President Donald Trump pulled the United States out of the accord in 2018 and reimposed U.S. sanctions, prompting Iran to begin violating its nuclear restrictions in 2019. His successor, Democrat Joe Biden, has sought a mutual return to compliance with the deal via indirect talks with Iran in which officials from other parties to the deal shuttle between them because Tehran refuses to meet directly with American officials. The other countries in the deal are Britain, China, France, Germany and Russia. Diplomats said they made significant progress in the six rounds of negotiations between April and June, when the talks took a five-month hiatus after the election of hard-line cleric Ebrahim Raisi as Iran"s president. During the seventh round, which began on Nov. 29, Iran abandoned any compromises it had made in the previous six, pocketed those made by others, and demanded more, a senior U.S. official has said. "We are losing precious time dealing with new Iranian positions inconsistent with the JCPoA or that go beyond it," the E3 diplomats said in their statement. "This is frustrating because the outline of a comprehensive and fair agreement that removes all JCPoA-related sanctions, while addressing our non-proliferation concerns, is clearly visible – and has been so since last summer," they added.