SEOUL, April 14 (Reuters) - North Korea said on Friday it has tested a new solid-fuel intercontinental ballistic missile (ICBM) Hwasong-18 to "radically promote" the country's nuclear counterattack capability, state media reported, warning of "extreme uneasiness and horror" to enemies.

North Korea fired what appeared to be a new model ballistic missile on Thursday, South Korea said, triggering a scare in northern Japan where Hokkaido residents were told to take cover, though there turned out to be no danger.

"The development of the new-type ICBM Hwasongpho-18 will extensively reform the strategic deterrence components of the DPRK, radically promote the effectiveness of its nuclear counterattack posture and bring about a change in the practicality of its offensive military strategy," KCNA said, using the initials of its official name.

Analysts said it would mark the North's first use of solid propellants in an intermediate-range or intercontinental ballistic missile.

Developing a solid-fuel ICBM has long been seen as a key goal for North Korea, as it could help the North deploy its missiles faster in the event of a war.

Leader Kim Jong Un guided the test, and warned it will make enemies "experience a clearer security crisis, and constantly strike extreme uneasiness and horror into them by taking fatal and offensive counter-actions until they abandon their senseless thinking and reckless acts".

North Korea has criticised recent U.S.-South Korean joint military exercises as escalating tensions and has stepped up weapons tests in recent months.

Most of the country's largest ballistic missiles use liquid fuel, which requires them to be loaded with propellant at their launch site - a time-consuming process.

"Solids are easier and safer for troops to operate in the field, and have a much smaller logistical train that makes field-deployed solid missile units harder to detect (and thus more survivable) than liquids," Vann Van Diepen, a former U.S. government weapons expert who now works with the 38 North project, said.

"But even liquids are highly survivable when field deployed," Van Diepen said, adding it depends on how North Korea chooses to operate the systems.

North Korea displayed what could be a new solid-fuel ICBM during a military parade in February after testing a high-thrust solid-fuel engine in December.

Analysts said the U.S. would be able to determine between a solid- or liquid-fueled launch via early warning satellites capable of detecting differences in the infrared data produced by different missile types.

The latest launch came days after Kim called for strengthening war deterrence in a "more practical and offensive" manner to counter what North Korea called moves of aggression by the United States.

The missile, fired from near Pyongyang, flew about 1,000 km (620 miles) before landing in waters east of North Korea, officials said.

North Korea said the test posed no threats to its neighbouring countries.