(Reuters) - The Western official tasked with preparing for a conference this year on ridding the Middle East of nuclear weapons said on Tuesday he had yet to secure the needed participation of all the region´s states, leaving it unclear when the event will be held.

The statement by Finnish diplomat Jaakko Laajava was a sign of the difficulties and sensitivities involved in getting Israel, its arch foe Iran and other Middle East nations to agree to sit around the same table to discuss the divisive issue.

Laajava, whose appointment was announced by the United Nations last October, did not say which countries were still leaving their possible attendance unclear, but both Iran and Israel are believed to be among them.

The plan for an international meeting in 2012 to lay the groundwork for the possible creation of a Middle East free of weapons of mass destruction was agreed to at a review conference on the nuclear Non- Proliferation Treaty (NPT) two years ago.

In his first public briefing on the issue since he took up the job, Laajava said he had held a series of meetings with regional states and they shared the goal of establishing such a zone but they differed on how and when to do so.

"Unfortunately, while much has de facto been already achieved in these consultations in terms of identifying common ground, I cannot yet report that the conference will be attended by all states of the region," he told an NPT meeting in Vienna.

Laajava said Finland was prepared to host the meeting any time during 2012, suggesting December was a possibility.

EGYPT WARNS AGAINST DELAY

Iran and Arab states see Israel´s assumed atomic arsenal as a major threat to peace and stability in the Middle East.

The Jewish state - widely believed to be the only regional state with such arms and the only one outside the NPT - and the United States regard Iran as the region´s main proliferation threat, accusing Tehran of seeking to develop such weapons.

Israel has said it would sign the NPT, a 1970 voluntary treaty to prevent the spread of atomic arms, and renounce nuclear weapons only as part of a broader Middle East peace deal with Arab states and Iran that guaranteed its security.

Israel does not rule out taking part in the planned conference, Foreign Ministry spokesman Yigal Palmor said last week, adding it was "awaiting clarification on some issues".

Thomas Countryman, U.S. assistant secretary for International Security and Non-Proliferation, told the meeting in Vienna that a Middle East free of weapons of mass destruction was an achievable, but long-term, goal.

But "a comprehensive and durable peace and full compliance by all countries in the region with their non-proliferation obligations" were needed for this to happen, he said

Continued efforts to "single out" Israel would make a conference increasingly less likely, Countryman added.

Iran´s delegate called for "sustained pressure" on the Jewish state to sign the NPT. Egypt said any delay in the Middle East conference would be a "major setback".

Mark Fitzpatrick, a director of the International Institute for Strategic Studies think-tank, said the rationale for creating a zone in the Middle East free of nuclear weapons and other weapons of mass destruction "is stronger than ever".

It could "be an answer to the Iranian nuclear crisis that threatens to spark regional proliferation and engulf the Middle East in another war" and "remove the sense of double standards over Israel´s nuclear program", Fitzpatrick said in a report. (Additional reporting by Dan Williams in Jerusalem; Editing by Alison Williams) (© Thomson Reuters 2012. 05/08/12)