Pyongyang expresses frustration over the slow progress of the lifting of sanctions while US insists on denuclearisation.

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 impoverished regime.

In a statement issued late on Friday, the North’s foreign ministry said Pyongyang could revert to its former policy if the US did not change its stance over sanctions.

“The word ‘byungjin’ may appear again and the change of the line could be seriously reconsidered,” said the statement carried by the official KCNA news agency.

For years, North Korea had pursued a “byungjin” policy of simultaneously developing its nuclear capabilities alongside the economy.

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”.

At an historic summit in Singapore in June, US President Donald Trump and Kim signed a vaguely worded statement on denuclearisation.

But little progress has been made since then, with Washington pushing to maintain sanctions against Pyongyang until its “final, fully verified denuclearisation”, and North Korea condemning US demands as “gangster-like”.

North Korea’s statement, released under the name of the director of the foreign ministry’s Institute for American Studies, also called for an end to US sanctions.

“The improvement of relations and sanctions are incompatible,” it said. “What remains to be done is the US corresponding reply.”

‘Double game’

The statement is the latest sign of Pyongyang’s increasing frustration with Washington.

Last month, North Korea’s state media carried a near 1,700-word-long commentary accusing the US of playing a “double game”, implicitly criticising Trump for his comments aimed at barring Seoul from lifting sanctions against Pyongyang.

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Despite a flurry of diplomacy on and around the Korean Peninsula, differences are emerging between South Korea and the US, which stations 28,500 troops in South Korea to protect it from its nuclear-armed neighbour.

South Korean President Moon Jae-in has long favoured engagement with North Korea, which is subject to multiple UN Security Council sanctions over its nuclear and ballistic missile programmes.

He has dangled large investment and joint cross-border projects as incentives for steps towards denuclearisation, while the US has been adamant pressure should be maintained on Pyongyang until it fully dismantles its weapons programmes.

In an interview with Fox News on Friday, US Secretary of State Mike Pompeo reiterated that sanctions will remain until Pyongyang carries out denuclearisation commitments made in Singapore, adding he will meet his North Korean counterpart next week.