North Korea on Tuesday called the US seizure of a North Korean cargo ship involved in banned coal exports a 'robbery' and demanded that the vessel be returned immediately.

The North's official Korean Central News Agency, or KCNA, carried a statement by an unnamed foreign ministry spokesman who accused the United States of betraying the spirit of a summit agreement last June between North Korean leader Kim Jong Un and President Donald Trump.

Kim and Trump agreed then to a vague statement calling for a nuclear-free Korean Peninsula and improved bilateral ties, but a second meeting between the leaders collapsed in February over mismatched demands in sanctions relief and disarmament.

The seizure of the cargo ship, which was announced last week, came at a delicate moment in US-North Korean ties, with North Korea resuming weapons tests that seem meant to force the United States to ease sanctions.

'The UN Security Council resolutions the United States mentioned as one of the reasons for robbing our trade vessel equate to a violent infringement of the sovereignty of our country and we have been entirely rejecting them,' the KCNA statement said.

'The United States should carefully consider what kind of consequences their daylight robbery could bring to the political situation and should send back our vessel without hesitation.'

Before the United States seized the cargo ship, the 581-foot vessel, named the Wise Honest, had first been detained by Indonesia in April 2018 while transporting a large amount of coal. It was brought Saturday to American Samoa, where it will undergo inspections.

North Korea is banned from exporting coal under U.N. sanctions toughened in 2017 to punish increasingly powerful weapons tests that year. Experts believe coal and other mineral exports help finance the North's weapons industry.