The North Korean leader, Kim Jong-un, oversaw the test of a “super-large multiple rocket launcher” on Saturday, the state news agency KCNA reported on Sunday.

North Korea fired what appeared to be two short-range ballistic missiles into the sea off its east coast, the South Korean military said, the latest in a series of launches in recent weeks amid stalled denuclearisation talks.

Photos released by North Korean state media showed rockets being launched from large tubes mounted on the back of an eight-wheel vehicle.

Analysts said it appeared to be at least the fourth new missile system unveiled by North Korea since denuclearisation talks stalled at a February summit between Kim and the US president, Donald Trump.

North Korea must step up development of strategic and tactical weapons to counter “ever-mounting military threats and pressure offensive of the hostile forces”, KCNA reported Kim saying on Saturday.

North Korea’s young defence scientists who developed the missiles are a “precious treasure and wealth of the country which cannot be bartered for anything”, Kim said.

On Saturday a KCNA commentary said North Korea “will never barter the strategic security of the country for the sanctions relief”.

North Korea fires a missile during the test of a multiple rocket launcher in an undisclosed location. Photograph: KCNA/Reuters

American officials have been trying to restart the stalled talks over its nuclear weapons and ballistic missile programs, which are heavily sanctioned.

After the latest tests, Trump again touted his good relationship with Kim and said Kim had been “pretty straight with me”.

Meanwhile South Korea began two days of military drills around a tiny island also claimed by Japan on Sunday, prompting a protest from Tokyo just days after Seoul scrapped an intelligence-sharing pact with its neighbour amid worsening relations.

Tokyo and Seoul have long been at loggerheads over the sovereignty of the group of islets called Takeshima in Japanese and Dokdo in Korean, which lie about halfway between the east Asian neighbours in the Sea of Japan, also known as the East Sea.

The Japanese foreign ministry said the drills were unacceptable and it had lodged a protest with South Korea calling for them to end.

Kenji Kanasugi, the director general at the ministry’s Asian and Oceanian affairs bureau, told the South Korean embassy in Tokyo that the island was “obviously an inherent part of the territory of Japan”.