SEOUL, Jan 28 (Reuters) - North Korea conducted tests of an upgraded long-range cruise missile and a warhead of a tactical guided missile this week, as leader Kim Jong Un visited a munitions factory producing a "major weapon system", state media KCNA said on Friday (Jan 28).

Tension has been simmering over North Korea's series of six weapons tests in 2022, among the largest number of missile launches it has made in a month, which triggered condemnation and a new sanctions push from the United States.

An update to a long-range cruise missile system was tested on Tuesday, and another test was held to confirm the power of a conventional warhead for a surface-to-surface tactical guided missile on Thursday, KCNA said.

Kim did not attend the tests, but during a visit to the munitions factory, he lauded "leaping progress in producing major weapons" to implement the ruling Workers' Party's decisions made at a meeting last month, a separate dispatch said.

"The factory holds a very important position and duty in modernising the country's armed forces and realising the national defence development strategy," Kim said.

KCNA did not specify the weapons or the factory's location. Kim called for bolstering national defences to tackle an unstable international situation at that party gathering.

Last week, North Korea said it would bolster its defences against the United States and consider resuming "all temporally-suspended activities", hinting at lifting a self-declared moratorium on testing nuclear bombs and intercontinental ballistic missiles (ICBMs).

At the factory, Kim called for "an all-out drive" to produce "powerful cutting-edge arms"," and its workers touted his devotion to "smashing ... the challenges of the US imperialists and their vassal forces" seeking to violate their right to self-defence, calling it "the harshest-ever adversity".

Pyongyang has defended missile launches as its sovereign right to self-defence and accused Washington and Seoul of applying "hostile policy" and double standards over weapons tests.

No ICBMs or nuclear weapons have been tested in North Korea since 2017 but a spate of shorter-range missile launches began amid stalled denuclearisation talks following a failed summit with the United States in 2019.

In Tuesday's test, two long-range cruise missiles flew 1,800km for 9,137 seconds and hit a target island off the east coast, showing practical combat performance, KCNA said.

The two tactical guided missiles tested on Thursday also precisely struck the target and proved the explosive power of their warhead as designed, it said.

The country "will keep developing powerful warheads capable of performing combat function and mission", KCNA added.

KCNA Photos dated on Tuesday showed a long-range missile launched from a transporter-erector-launcher, gushing flame, before sparking a fire on an island. Another set of images from Thursday showed a shorter-range missile rising into the sky above a cloud of dust and then hitting an island.

South Korea's Joint Chiefs of Staff (JCS) said it detected both tests, and the short-range missiles fired from the eastern coastal city of Hamhung travelled for about 190km to an altitude of 20km.

This month alone, North Korea has also tested tactical guided missiles, two "hypersonic missiles" capable of high speed and manoeuvring after lift-off, and a railway-borne missile system.