Dozens of world leaders are to gather in Washington next week for an unprecedented meeting on nuclear security, and U.S. President Barack Obama hopes they can agree on how to keep atomic bombs out of terrorists' hands.

Although the gathering of 47 countries will not focus on individual nations, the nuclear programs of Iran and North Korea are expected to come up in Obama's bilateral meetings with Chinese President Hu Jintao and other leaders.

Hu's decision to attend the summit, Western diplomats said, was a major victory for Obama, because it indicates that Beijing does not want bilateral tensions over Taiwan and other issues to cripple Sino-U.S. relations and co-operation on other key security and foreign policy topics.

Early today, however, Israeli Prime Minister Benjamin Netanyahu cancelled his country's participation.

He made the decision after learning Egypt and Turkey intended to raise the issue of Israel's presumed nuclear arsenal at the conference, a senior government official said.

Israel is believed to be the only nuclear-armed power in the Middle East but has never confirmed or denied that it possesses atomic weapons. It has not signed the nuclear non-proliferation treaty.

A draft communiqué circulated to countries attending the summit includes a U.S. proposal to "secure all vulnerable nuclear material in four years." The draft text will likely be revised before it is adopted at the end of the April 12-13 meeting.