The paper, drafted by the Joint Chiefs of Staff of the U.S. Armed Forces, also revealed that submarines which make port calls in Yokosuka, Sasebo and Okinawa in Japan are prepared for reloading nuclear warheads if necessary to deal with a crisis.

The March 15 draft paper, a copy of which was made available, is titled "Doctrine for Joint Nuclear Operations" providing "guidelines for the joint employment of forces in nuclear operations...for the employment of U.S. nuclear forces, command and control relationships, and weapons effect considerations."

"There are numerous nonstate organizations (terrorist, criminal) and about 30 nations with WMD programs, including many regional states," the paper says in allowing combatant commanders in the Pacific and other theaters to maintain an option of preemptive strikes against "rogue" states and terrorists and "request presidential approval for use of nuclear weapons" under set conditions.

The paper identifies nuclear, biological and chemical weapons as requiring preemptive strikes to prevent their use.

But allowing preemptive nuclear strikes against possible biological and chemical attacks effectively contradicts a "negative security assurance" policy declared by the U.S. administration of President Bill Clinton 10 years ago on the occasion of an international conference to review the Nuclear Non-Proliferation Treaty.

Creating a treaty on negative security assurances to commit nuclear powers not to use nuclear weapons against countries without nuclear weapons remains one of the most contentious issues for the 35-year-old NPT regime.

A JCS official said the paper "is still a draft which has to be finalized," but indicated that it is aimed at guiding "cross-spectrum" combatant commanders how to jointly carry out operations based on the Nuclear Posture Review report adopted three years ago by the administration of President George W. Bush.

Citing North Korea, Iran and some other countries as threats, the report set out contingencies for which U.S. nuclear strikes must be prepared and called for developing earth-penetrating nuclear bombs to destroy hidden underground military facilities, including those for storing WMD and ballistic missiles.

"The nature (of the paper) is to explain not details but cross spectrum for how to conduct operations," the official said, noting that it "means for all services, Army, Navy, Air Force and Marine."

In 1991 after the end of the Cold War, the United States removed its ground-based nuclear weapons in Asia and Europe as well as strategic nuclear warheads on warships and submarines.

But the paper says the United States is prepared to revive those sea-based nuclear arms.

"Nuclear-armed sea-launched cruise missiles, removed from ships and submarines under the 1991 Presidential Nuclear Initiative, are secured in central areas where they remain available, if necessary for a crisis," the paper says.

The paper also underlined that the United States retains a contingency scenario of limited nuclear wars in East Asia and the Middle East.

"Geographic combatant commanders may request presidential approval for use of nuclear weapons for a variety of conditions," the paper says.

The paper lists eight conditions such as "an adversary using or intending to use WMD against U.S. multinational or alliance forces or civilian populations" and "imminent attack from adversary biological weapons that only effects from nuclear weapons can safely destroy."

The conditions also include "attacks on adversary installations including WMD, deep, hardened bunkers containing chemical or biological weapons" and countering "potentially overwhelming adversary conventional forces."