SEOUL, May 31 (Reuters) - North Korea says it fired 18 short-range ballistic missiles during a drill as a demonstration of its willingness to launch a pre-emptive strike against South Korea's "gangsters' regime" if necessary to counter an attack, state media reported on Friday.

North Korean leader Kim Jong Un guided the firing drill of 600mm "super-large" multiple rocket launchers on Thursday, state news agency KCNA reported.

The report came after South Korea said it detected at least 10 short-range ballistic missiles fired by North Korea off its east coast, and called it a possible display for would-be buyers, including Russia.

Artillery troops successfully hit the target of an island located about 365 kms (227 miles) away as leader Kim oversaw the demonstration at the launch site, KCNA reported.

Photos published by state media showed 18 missiles, known by experts as KN-25s, rising into the air from mobile launchers.

First tested in 2019, the “super-large” rocket blurs the distinction between multiple-launch rocket systems (MLRS) and SRBMs, according to the Center for International and Strategic Studies.

North Korea has said a tactical nuclear weapon could be fitted to such missiles.

Kim urged readiness by the country's nuclear force to carry out the mission of war deterrence as well as taking the initiative in case of war, the report added.

"Showers of fire for annihilation" during the drill showed North Korea's will to defend its sovereignty and react against the enemy, a later KCNA report about the event in English said.

The drill included the use of a recently unveiled fire-control system that is part of the government's combined nuclear weapons management system, KCNA said.

Thursday's launch using ballistic missile technology was condemned by the U.S. State Department as reckless and violating multiple U.N. Security Council resolutions.

The U.S. Defense Intelligence Agency said analysis of debris imagery confirms Russia has fielded North Korean missiles in its war in Ukraine, according to a report summary released on Friday.

Russia and North Korea have denied arms deals, which would violate U.N. embargoes on Pyongyang, but have vowed to deepen cooperation in all sectors.

A separate column carried by KCNA on Friday criticised the deployment of U.S. RC-135U reconnaissance aircraft from Japan to the Korean peninsula on Wednesday, saying the aircraft and other reconnaissance assets by the South and the U.S. infringed on North Korea's sovereignty.

South Korean media reported that a U.S. military spy plane flew above the Seoul metropolitan area and waters off the west coast this week, citing flight trackers.

On Wednesday, North Korea sent hundreds of balloons carrying trash and manure across the heavily fortified border to South Korea, calling them "gifts of sincerity", prompting an angry response from Seoul, which said the act was base and dangerous.

Photo from Reuters