* Iran to grant access to uranium mine, heavy water plant
* Agreement comes as powers seek diplomatic breakthrough
* Makes no direct mention of probe into suspected bomb research
* Welcome first step but implementation key - experts (Adds IAEA to visit Arak soon, December talks, paragraph 17)
By Fredrik Dahl and Marcus George
VIENNA/DUBAI, Nov 11 (Reuters) - Iran will grant U.N. inspectors "managed access" to a uranium mine and a heavy-water plant within three months as part of a cooperation pact reached on Monday that aims to allay concern about Tehran's nuclear programme.
It was signed by U.N. nuclear agency chief Yukiya Amano in Tehran after Iran and six world powers came close to a preliminary nuclear agreement during broader talks in Geneva at the weekend and decided to meet again on Nov. 20.
The sets of negotiations are separate but both centre on fears that Iran may be seeking the capability to build nuclear weapons, a charge it denies. The Iran-IAEA deal may encourage hopes for next week's resumption of big power diplomacy after a decade of international deadlock on the issue.
"This is an important step forward to start with, but much more needs to be done," Amano said in the Iranian capital.
The International Atomic Energy Agency (IAEA) and Iran will "strengthen their cooperation and dialogue aimed at ensuring the exclusively peaceful nature of Iran's nuclear programme," a joint statement said.
"It was agreed that Iran and the IAEA will cooperate further with respect to verification activities to be undertaken by the IAEA to resolve all present and past issues."
That seemed in part to be a reference to a stalled IAEA investigation into suspected atomic bomb research by Iran, but it gave no detail on when and how that probe may resume.
Amano suggested such issues would be addressed in "subsequent steps" under the IAEA-Iran framework accord.
Britain - which is negotiating with Tehran along with the United States, France, Germany, China and Russia - welcomed the agreement. It was "important that Iran addresses the substance of the agency's concerns about possible military dimensions" to the nuclear programme, it said.
Iran expert Ali Vaez of the International Crisis Group think tank said: "This goodwill gesture is likely to put Iran in a better position when its negotiators meet again with their (six power) counterparts next week in Geneva."
Middle East specialist Shashank Joshi at the Royal United Services Institute in London said much would depend on implementation: "We have had numerous false starts before."
The Vienna-based IAEA, which regularly inspects Iranian nuclear sites, has long requested more information and wider access to fulfil its mandate to supervise Iran's nuclear programme to ensure there are no military links.
Iran had until now ignored several requests. But the election of a relative moderate, Hassan Rouhani, as Iranian president in June has fuelled hopes that Iran's nuclear dispute with the West can be resolved peacefully.
NO MENTION OF PARCHIN ACCESS
An annex to the IAEA agreement listed six steps to be taken by Feb. 11, including access to the Gchine uranium mine and a heavy-water production plant near the town of Arak.
Under the accord on boosting nuclear transparency, Iran would also provide information about planned new research reactors and sites for future nuclear power plants, as well as clarify earlier statements about additional uranium enrichment facilities it has said it plans to build.
Amano said the agreed steps were "substantive" measures.
After a follow-up meeting between senior IAEA and Iranian experts in Tehran, they said in a statement that the U.N. agency would visit the Arak facility "in the near future" and that a new meeting would be held on Dec. 11 in Vienna.
The IAEA last visited the plant - which produces heavy water for a nearby research reactor under construction - more than two years ago and now monitors it via satellite images.
The Arak reactor is of deep concern for the West as it may yield plutonium, a potential bomb fuel, once it starts up. Iran says it will make isotopes for medical and agricultural use.
The Gchine mine is located near the Gulf port of Bandar Abbas and its annual output is estimated at around 21 tonnes of uranium. When refined, this can be used to fuel power plants but also to build nuclear weapons if enriched much further.
Nuclear expert Mark Hibbs of the Carnegie Endowment think-tank described Monday's agreement in principle as positive.
"The details will have to be negotiated for specific facilities and cases, and success may ultimately depend on the atmospherics of Iran's relationship with the powers," he said.
Iran says its nuclear programme is a peaceful bid to generate electricity. But its refusal to halt sensitive work has drawn tough sanctions targeting its lifeblood oil exports.
The statement with the IAEA represents "a road map that specifies bilateral steps in relation to resolving outstanding issues," the head of Iran's atomic energy organisation, Ali Akbar Salehi, said at the news conference in Tehran with Amano.
The agreement, however, made no explicit mention of the IAEA's investigation into what it calls possible military dimensions to Iran's nuclear programme, including long-sought access to the Parchin military base where the agency suspects nuclear-related explosives tests took place a decade ago. (Editing by Giles Elgood and Peter Graff)