Beijing wants an official and more clear-cut explanation from Washington about its decision to list China among the countries it is targeting with nuclear weapons.
The Foreign Ministry had earlier expressed China's deep shock at being named on a secret Pentagon plan detailing the possible targets and circumstances under which the United States might use its nuclear arsenal.
Foreign Ministry spokesman Sun Yuxi said he was not satisfied with explanations from Secretary of State Colin Powell and National Security Adviser Condoleezza Rice that the US did not plan to use nuclear weapons.
'We are now waiting for the US side to offer up further more formal and clear explanations,' Mr Sun said, adding China and the US had an agreement not to target each other with nuclear weapons.
The Pentagon study made it clear that despite two presidential summits in six months, Washington still viewed China as a potential future military adversary.
The secret 'nuclear posture review' passed to the US Congress by the Pentagon in January outlined the possible use of nuclear weapons against countries that possess or are developing weapons of mass destruction. Apart from China, the countries listed are Libya, Syria, Russia, Iran, Iraq and North Korea. One of the situations in which the US use of nuclear weapons is envisaged is a conflict over Taiwan.