The United Nations is studying a letter sent by North Korea over the U.S.' recent seizure of a North Korean cargo ship.

The North's state media Korean Central News Agency reported on Saturday that North Korean Ambassador to the UN Kim Song sent the letter to UN Secretary-General Antonio Guterres, calling for "urgent measures" to deal with the seizure.

Stephane Dujarric, spokesperson for the UN chief, confirmed the receipt of the letter on Monday, saying that the letter has been "distributed and circulated as requested as a document of the Security Council." 

The spokesperson told a press briefing that the UN is studying the letter as it relates to the issue of sanctions on North Korea and actions taken in the implementation of the sanctions. 

Dujarric added that questions related to possible sanctions evasion and the UNSC member states' implementation of Security Council resolutions are matters for member states to address.

North Korea said in the letter that the seizure of the ship "Wise Honest" clearly indicates the U.S. is a “gangster country” that does not care about international laws. It added the U.S. committed a "sovereignty-infringing act" by flagrantly violating the UN Charter when it dispossessed a cargo ship where the North's sovereignty is fully exercised.