SEOUL • The US State Department has cleared US$314 million (S$430 million) in possible sales of air defence missiles to South Korea, the Pentagon said, as tensions re-emerge on the Korean peninsula.

South Korea, a key Asian ally of the United States, has asked to buy up to 94 SM-2 missiles used by ships against air threats, along with 12 guidance systems and technical assistance for a total cost of US$313.9 million, the US Defence Security Cooperation Agency (DSCA) said on its website last week.

The agency, a unit of the Department of Defence, delivered certification on Thursday notifying Congress of the possible sale.

The proposed sale comes after North Korea recently criticised South Korea's defence purchases from the US, including the arrival of the first F-35 stealth aircraft.

The reclusive North and the rich, democratic South are technically still at war because their 1950-53 conflict ended in a truce instead of a peace treaty.

South Korea already uses SM-2 missiles developed by Raytheon, but is building more missile defence-capable destroyers equipped with the weapon.

The proposed sale comes after North Korea recently criticised South Korea's defence purchases from the United States, including the arrival of the first F-35 stealth aircraft.

North Korea, on its part, has boasted about its indigenous surface-to-air missiles.

Japan, another key US ally in the region, was also cleared to buy US$317 million worth of medium-range air-to-air missiles from Washington, the DSCA said.

Meanwhile, North Korea has asked United Nations secretary-general Antonio Guterres to deal with the "illegal" seizure of one of its cargo ships by the US, state media said yesterday.

"This act of dispossession has clearly indicated that the United States is indeed a gangster country that does not care at all about international laws," the North Korean ambassador to the UN said in a letter sent to Mr Guterres dated Friday, according to North Korea's KCNA news agency.

Pyongyang's protest to the UN over the seizure comes amid mounting tensions since a second summit between North Korean leader Kim Jong Un and US President Donald Trump, aimed at bringing about the denuclearisation of the North, broke down in Hanoi in February.

The letter also called for "urgent measures" by Mr Guterres and claimed that Washington infringed the North's sovereignty and violated UN charters.

With the denuclearisation talks stalled, North Korea went ahead with more weapons tests this month.

The tests were seen as a protest by Mr Kim after Mr Trump rejected his calls for sanctions relief at the Hanoi summit.

North Korea has said the ship seizure violated the spirit of the summit and demanded the return of the vessel without delay.

The US Justice Department said the North Korean cargo ship, known as the "Wise Honest", was seized and impounded to American Samoa. It is said that the vessel was involved in illicit coal shipments in violation of sanctions.

The ship was first detained by Indonesia in April last year.

REUTERS