The United States has sent a top official to Israel amid an effort to revive talks on a Middle East zone free of nuclear weapons, a central issue of a landmark treaty review conference that some fear will end Friday without progress on global disarmament.

The State Department confirmed that the assistant secretary of state for international security and nonproliferation was in Israel to discuss the issue. An Israeli Foreign Ministry spokesman declined comment on Thomas Countryman's visit, saying it was a "very sensitive" matter.

Establishing a zone free of nuclear weapons in one of the world's most tense regions is a rare point of agreement between the United States and Russia these days. Frustrated by the delay of a conference on the zone that was supposed to take place three years ago, Russia has proposed that U.N.-led talks be held no later than March 2016.

A draft proposal by a review conference subcommittee on regional issues, dated Wednesday, would impose an even earlier deadline, saying the U.N. secretary-general should convene talks by Dec. 15 if Israel and its neighbours can't agree on arrangements by then.

That has alarmed Israel, which is not a party to the treaty and has never publicly declared what is widely considered to be an extensive nuclear weapons program. Israel was furious when the United States at the treaty review conference five years ago signed off on a document that called for talks on a Middle East nuclear-free zone by 2012.

With a new document that threatens to pressure Israel again, the U.S. visit this week is meant to calm things down. "This administration and this president do not break commitments to our Israeli partners, and any suggestion to the contrary is offensive," White House spokeswoman Bernadette Meehan said in a statement.

Israel is concerned about talks being held without its agreement on an agenda, said Emily Landau, head of the Arms Control program at the Institute for National Security Studies, an Israeli think-tank . If talks single out Israel as the only state that needs to take action, "obviously it's not something Israel will be able to agree to," she said.

On Thursday, U.S. State Department spokeswoman Marie Harf said the U.S. was "working to ensure that a final text meets our interests and Israel's." She stressed that the U.S. and Israel share the goal of a Middle East free of weapons of mass destruction.

The review conference for the landmark Nuclear Non-Proliferation Treaty takes place just every five years, and a failure to agree on a way forward would highlight the growing frustration of countries without nuclear weapons to get the nuclear-armed ones to take concrete steps to disarm. The United States and Russia hold more than 90 per cent of the estimated 16,000 nuclear weapons in the world today.

Israel showed up at the review conference this year as a surprise observer. It blamed its Arab neighbours for the failure of progress toward achieving a Middle East free of nuclear weapons, saying that after five rounds of consultations with some of its neighbours in Switzerland between October 2013 and June 2014 on a possible agenda, the other states discontinued the meetings.

Israel did not say why the talks were discontinued but noted that they were "the first direct engagement between Israel and its neighbours on this issue in over 20 years."

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Associated Press writers Daniel Estrin in Jerusalem and Bradley Klapper in Washington contributed.