WASHINGTON—Plans for a United Nations-backed conference aimed at ridding the Middle East of nuclear weapons are unraveling because of political upheaval in the region and diplomatic sparring over suspected nuclear-weapons programs in Iran and Israel, said officials involved in the event´s preparations.

The conference, tentatively set for December in Helsinki, would mark the first meeting of Mideast states solely focused on establishing a nuclear-weapons-free zone in the region.

The gathering is seen as crucial to sustaining and strengthening the U.N.´s Nuclear Nonproliferation Treaty, the primary international vehicle for reducing the threat posed by nuclear arms. Arab states have warned in recent months that they may be unwilling to commit to abiding by the NPT if the Mideast conference doesn´t take place to address the threats they see from Iran´s and Israel´s suspected programs.

A Finnish diplomat overseeing the convening of the conference said in an interview on Thursday that he has yet to receive commitments from some of the region´s key players to attend the conference.

"The participation of all countries is a prerequisite for a successful conference. But for some countries...their participation remains an open question," Jaakko Laajava said via telephone from Finland. "But no country in the region has yet rejected the call for this conference."

Mr. Laajava wouldn´t specify the countries that haven´t committed. Israel has said publicly in recent weeks that it may be unable to attend the Helsinki meeting due to the region´s drastically shifting security environment in the wake of revolutions in Syria, Egypt and Libya.

Iran, meanwhile, has expressed doubts about the utility of the conference, growing out of its skepticism that Western governments would seriously press Israel to disarm.

The Jewish state is believed to have a nuclear-weapons arsenal consisting of hundreds of warheads, but has neither confirmed nor denied their existence under a policy known as "nuclear ambiguity." The U.S. and the European Union charge Iran with clandestinely seeking to build atomic weapons, a charge Tehran denies.

"When the decision to hold this conference was adopted back in May 2010, the Middle East was quite a different place, to put it mildly," Israel´s foreign ministry spokesman, Yigal Palmor, said Thursday. "I believe that the chances to get this thing going now have not exactly been improved by regional circumstances."

Discussions on establishing a Middle East free of nuclear weapons have dated back to the 1970s, when Arab states sought to diminish Israel´s perceived military superiority.

The idea gained traction in 1995 when the U.S., U.K. and Russia supported the initiative as part of a diplomatic push at the U.N. to gain Arab support for an indefinite extension of the NPT´s ratification. In 2010, the NPT´s signatory states for the first time committed to hosting a conference on the Middle East zone, which was set for 2012.

Mr. Laajava, the Finnish foreign ministry´s undersecretary of state, said he has held hundreds of meetings with potential conference participants in the past seven months, including meetings with senior Iranian, Israeli, Syrian and Egyptian officials. This week, he addressed a gathering in Vienna of NPT signatory states preparing for the 2015 conference that will review the implementation of the treaty.

"This was the first time the NPT countries had a chance...to receive my report on the conference," Mr. Laajava said. "I must say I was encouraged by the tone of the assessment."

Still, the Obama administration, which has supported the conference, is also voicing growing doubts that it will be held on schedule. U.S. officials said this week they remain concerned that any event in Helsinki could morph into a venue largely aimed at attacking Israel´s nuclear record. And they said they are skeptical much progress can be made without first addressing concerns about Iran´s nuclear program.

"Failing to acknowledge and address the underlying political and security realities in the region will diminish the prospects for a successful conference in Helsinki," the State Department´s assistant secretary for international security and nonproliferation, Thomas Countryman, said Tuesday in Vienna.

The five permanent members of the U.N. Security Council, plus Germany, are meeting with Iran´s nuclear negotiators in Baghdad on May 23 to try to address international concerns about Tehran´s nuclear advances. (Copyright © Dow Jones & Company, Inc.) 05/11/12)