North Korea has warned it could revive a state policy aimed at strengthening its nuclear arsenal if the United States does not lift economic sanctions against the country.<br />''<br />''The statement released by its Foreign Ministry yesterday said it could bring back its policy of simultaneously advancing its nuclear force and economic development.<br />''<br />''Pyongyang accused Washington of derailing commitments made by both the leaders at their June summit in Singapore to work toward a nuclear-free Korean Peninsula, without describing how and when it would occur.<br />''<br />''<span style="color: #222222;">Friday's statement marked the first time the North said it could potentially resume weapons tests and other development activities since Kim's signalled a new state policy in April.</span><br />