SEOUL, July 14 (Reuters) - North Korean leader Kim Jong Un has sacked or demoted some senior officials for their "irresponsible" handling of his flagship project to build a new town in the country's north, state media KCNA said on Sunday.

Kim announced the decision while visiting Samjiyon, where North Korea has been building what it called a "socialist utopia" and "a model of highly-civilised mountain city" with new apartments, hotels, a ski resort and commercial, cultural and medical facilities.

While praising builders for their achievements so far, Kim said the irresponsibility of senior officials had caused a series of serious deviations including poor construction work and financial losses.

He singled out Ri Sun Chol, minister of state construction control who was appointed in September, as a "good-for-nothing person" who has never even been to the site since December, suspending him and calling for a formal investigation.

Kim also suspended all members of a construction inspection committee for the project, demoted a ruling Worker's Party official responsible for the matter, and vowed to reexamine vice premier and others over their neglect of duty.

"Going round the newly-built hotels for domestic tourists, he severely pointed out that their construction was carried out at an outdated and backward level," KCNA quoted Kim as saying.

"Those new buildings have to be remodelled and, consequently, this problem badly affects the general long-term plan for the city development, bringing economic losses."