<span style="color: #222222;">North Korea has warned the United States it will seriously consider returning to a state policy aimed at building nuclear weapons if Washington does not end tough economic sanctions against the regime. </span><br />'' <br />'' <span style="color: #222222;">For years, the North had pursued a byungjin policy of simultaneously developing its nuclear capabilities alongside the economy. </span><br />'' <br />'' <span style="color: #222222;">In April, citing a fresh climate of detente and peace on the peninsula, North Korean leader Kim Jong Un declared the nuclear quest complete and said his country would focus on socialist economic construction. </span><br />'' <br />'' <span style="color: #222222;">But a statement issued by the North's foreign ministry said Pyongyang could revert to its former policy if the US did not change its stance over sanctions. </span><br />'' <br />'' <span style="color: #222222;">At a historic summit in Singapore in June, US President Donald Trump and Kim signed a vaguely-worded statement on denuclearisation.</span><br />''