* High-level IAEA team expected in Iran in late January
* Iran says willing to discuss U.N. nuclear suspicions
* Western diplomats suspect another stalling tactic (Adds analyst comment on assassination, detail, edits)
By Fredrik Dahl
VIENNA, Jan 13 (Reuters) - Iran will need to show genuine readiness to address mounting suspicions about its nuclear programme at rare talks with senior U.N. officials this month to convince a sceptical West that it is not just stalling.
With Iran facing intensifying sanctions pressure, a high-level team from the U.N. atomic watchdog is expected to visit this month, seeking explanations on long-standing concerns that Iran may be trying to develop nuclear weapons capability.
Iran's envoy to the International Atomic Energy Agency (IAEA) has said the Islamic Republic is ready to answer the agency's questions in order to remove "any ambiguities" about its nuclear work and clear up the issue once and for all.
But Iranian officials have used such language before, and diplomats say this will not be enough to satisfy the IAEA.
"I would tend to be rather pessimistic," one Western envoy said. "This road is paved with danger and past experience cannot render anyone optimistic."
Another diplomat added: "I doubt very seriously that (the high-level U.N. nuclear mission) will lead to anything."
Iran rejects as forged accusations that it has coordinated efforts to process uranium, test high explosives and revamp a ballistic missile cone to accommodate a nuclear warhead.
But while U.N. inspectors regularly monitor Iran's declared nuclear facilities, their movements are otherwise restricted, and the IAEA has complained for years of a lack of access to sites, equipment, documents and people relevant to its probe.
"They (the Iranians) should understand that they don't get rid of these questions by not addressing them. This is something the IAEA will definitely tell them," a Western official said.
But this week's assassination of a nuclear scientist in Iran, which Tehran blamed on Israel, gives Iranian officials an "excuse to stonewall access to its scientific community and subvert the agency's efforts," two nuclear experts said.
"If the IAEA loses some of its access, the world will have markedly less information about Iran's nuclear programme, which will make the goal of taming Iran's atomic ambitions more difficult," Ali Vaez and Charles Ferguson of the Washington-based Federation of American Scientists wrote in a comment.
Daryl Kimball of the U.S.-based Arms Control Association said it was critical to secure "more intrusive access by the IAEA to all of Iran's nuclear-related activities" and convince it to finally address questions about weapons-related work.
"The IAEA needs this increased access to detect and deter any clandestine nuclear activities," he said in a comment.
Iran says its nuclear work is purely peaceful, and has shown no substantial sign of changing its position.
But its leadership has come under pressure since the IAEA reported in November, in a detailed 14-page document, that Tehran appeared to have worked on designing a nuclear weapon and that secret research to that end may be continuing.
Iran has also stoked Western suspicions by starting to enrich uranium deep inside a mountain at Fordow.
European Union countries are now preparing a partial embargo on Iranian oil to follow similar U.S. measures, and Iran has threatened to retaliate by blocking Gulf oil shipping lanes.
But Tehran has also signalled readiness to resume talks with big powers over its nuclear programme that have been frozen for a year over its refusal to discuss suspending enrichment.
The IAEA's chief safeguards inspector, Herman Nackaerts, Assistant Director General Rafael Grossi and other senior officials will probably visit Tehran around Jan. 28, although this has not yet been finalised, diplomats say.
"The Iranians don't have much to lose by holding these talks," the Western official said. "For the Iranians, I believe it is important to have good relations with the IAEA."
(Editing by Mark Heinrich)