North Korean leader Kim Jong-Un visited a newly completed ski resort Tuesday and ordered officials to open his pet project to the public as soon as possible, state media reported.

Kim took a test ride on a ski lift at the Masik Pass Ski Resort, which he said during a visit two weeks ago was "at the centre of the world's attention", the Korean Central News Agency (KCNA) said.

North Korea is purging officials who had been close to Jang Song-Thaek, the once-powerful uncle of leader Kim Jong-Un who was executed this month, a South Korean minister said Monday.

Jang, once the North's unofficial number two and Kim's political mentor, was executed on December 12 on a array of charges including treason and corruption.

North Korea's ambassador to Sweden has been recalled apparently as part of a purge prompted by the execution of the once-powerful uncle of leader Kim Jong-Un, a report said Friday.

Pak Kwang-Chol, an associate of the young supremo's uncle and political regent Jang Song-Thaek, was seen returning home after making a brief stopover in Beijing, South Korea's Yonhap news agency said.

South Korea Thursday slammed North Korea for issuing a "rude" questionnaire which urged President Park Geun-Hye to choose between peace and confrontation.

The South's Unification Ministry said instability was growing in and around the Korean peninsula because of Pyongyang's "unethical and irrational" attitude.

North Korean leader Kim Jong-Un has urged the country's military to bolster its combat readiness, saying a war could break out "without any prior notice", state media reported Wednesday.

The call comes at a time of heightened tension on the Korean Peninsula following the execution of Kim's uncle and former mentor in an unusually public purge.

South Korea's president Tuesday warned Seoul would react "mercilessly to any provocations" from the North, describing the situation over the border as "ominous" as she visited a frontline guard post.

Seoul and Washington have been increasingly concerned over the stability of the North Korean regime following the execution two weeks ago of Jang Song-Thaek, a high-level official and uncle of young leader Kim Jong-Un.

Satellite imagery suggests North Korea is making "wide-ranging, extensive" efforts to fully reactivate its main nuclear complex, a U.S. think tank said Tuesday, in line with Pyongyang's vows to strengthen its weapons program.

Recent images show work at the Yongbyon nuclear compound apparently aimed at producing fuel rods to be used in a plutonium reactor, Johns Hopkins University's U.S.-Korea Institute said.

The shock purge and execution of the North Korean leader's uncle stemmed from his attempts to take control of the country's lucrative coal export business, South Korea's spy chief told lawmakers Monday.

Jang Song-Thaek, the once-powerful uncle and political regent to young leader Kim Jong-Un, was executed on December 12 on charges which included plotting a coup and corruption.

North Korea has threatened a "merciless" strike against the South after activists burned effigies of the ruling Kim dynasty on the second anniversary of the death of former leader Kim Jong-Il, officials said Friday.

The warning was contained in a message sent Thursday by the secretariat of the National Defense Commission, the North's highest military body, through a military hotline, the South's defense ministry said.

The two Koreas on Thursday held their first meeting since the shock execution of North Korean leader Kim Jong-Un's uncle, resuming talks about a joint industrial park as concerns rise over instability in Pyongyang.

The last round of such talks took place in September when the Kaesong industrial zone, just over the border in North Korea, reopened after military tensions caused a five-month closure.