The United States has sent a top official to Israel in an effort to revive talks on a Middle East zone free of nuclear weapons, a central issue of a nuclear 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 Middle East zone free of nuclear weapons is a rare point of agreement between the United States and Russia.