(Reuters) - France, Britain and Germany on Saturday said they had "serious doubts" about Iran's intentions to revive a nuclear deal, comments that were rejected by Tehran and called "very untimely" by Moscow.

Iran earlier this month sent its latest response to the European Union's proposed text to restore the 2015 agreement under which Tehran had restrained its nuclear programme in exchange for relief from U.S., EU and U.N. economic sanctions.

Diplomats have said Iran's response to the EU coordinator was a step backwards, with it seeking to link a revival of the deal with the closure of investigations by the International Atomic Energy Agency (IAEA) into uranium traces at three sites.

The IAEA's Board of Governors meet on Monday, three months after adopting a resolution urging Iran to give credible answers to the watchdog on the issue. Ahead of that meeting the European parties to the deal vented their frustration.

"This latest demand raises serious doubts as to Iran's intentions and commitment to a successful outcome on the JCPoA," the three countries, known as the E3, said in a statement, referring to the deal's full name, the Joint Comprehensive Plan of Action.

"Iran's position contradicts its legally binding obligations and jeopardises prospects of restoring the JCPoA."

Iran's Foreign Ministry spokesperson Nasser Kanaani said the statement was "unconstructive", adding "the three European countries are advised to play a more active role in providing solutions to end the few disagreements that remain", state media reported.