"First use" has been unthinkable for years
Quoting a secret Pentagon report, the Los Angeles Times newspaper names China, Russia, Iraq, North Korea, Iran, Libya and Syria as potential targets.
The Pentagon has declined to comment on the report which analysts have described as "dynamite".
According to the paper, the report lists three situations in which the weapons could be used.
These include "retaliation for attack with nuclear, biological or chemical weapons" and "against targets able to withstand non-nuclear attack".
The third category - "in the event of surprising military developments" - is described by the BBC's Washington correspondent, Paul Reynolds, as a "catch-all" clause.
The paper says the report was presented by the Pentagon to members of Congress on Friday.
It is quoted as saying the Pentagon should be ready to use nuclear weapons in an Arab-Israeli conflict, a war between China and Taiwan and an attack by North Korea on the South.
As for Russia, the report says that it is only listed in view of its own large nuclear arsenal and it is not viewed as an enemy.
'Taboo lifted'
Defence analysts told the Los Angeles Times that the secret report appeared to mark the first time an official list of target countries had come to light.
"I can imagine what these countries are going to be saying at the UN," said Joseph Cirincione, a nuclear arms expert at the Carnegie Endowment for International Peace in Washington.
The report clearly referred to nuclear arms as a "tool for fighting a war, rather than deterring them", he added.
Anti-nuclear campaigners pointed out that the reported instruction to build new tactical nuclear weapons indicated that the administration of George W Bush was more willing to lift the old taboo on using nuclear weapons except as a last resort.
"This is very, very dangerous talk," said John Isaacs, president of the Council for a Livable World.
"Dr Strangelove is clearly still alive in the Pentagon," he commented, referring to a 1964 feature film about a nightmare nuclear conflict between the US and the Soviet Union.
Our correspondent recalls that the US made a veiled threat to Iraq during the Gulf War that it could respond with nuclear weapons to an attack by Baghdad using chemical or biological weapons.