North Korean leader Kim Jong-Un has urged his army to prepare for war with the United States and its allies, state media said Saturday, as Pyongyang ramps up the rhetoric ahead of U.S.-South Korea military drills.

Kim's comments came after South Korea and the United States Friday conducted a joint naval drill involving 10 South Korean warships and a U.S. Aegis destroyer, ahead of the launch of large-scale military exercises that have enraged the North.

North Korea vowed to wage a "merciless, sacred war" against the United States on Thursday, days before the launch of annual joint South Korea-U.S. military exercises that have incensed Pyongyang.

"Nuclear weapons are not a monopoly of the U.S.," the ruling party's official newspaper, Rodong Sinmun, warned in an editorial carried by the state KCNA news agency.

North Korea has managed to evade U.N. sanctions targeting a key shipping company by renaming and reflagging vessels which continue to operate, a U.N. report said Wednesday.

A panel of experts also reported to the Security Council that North Korean diplomats, officials and trade representatives are playing key roles in the trade of arms and ballistic-related items, in violation of U.N. resolutions.

North Korea appears poised to expand its nuclear program over the next five years and in a worst case scenario could possess 100 atomic arms by 2020, U.S. researchers warned Tuesday.

And cutting-edge European companies could be unwittingly contributing to Pyongyang's suspect nuclear program with their equipment diverted to the isolated country via China, they said.

The once powerful aunt of North Korean leader Kim Jong-Un is still alive despite her extended absence from public view since her husband was executed, South Korea's spy agency said Tuesday.

The whereabouts and status of Kim Kyong-Hui, 68, have been a focus of media attention after her husband Jang Song-Thaek was executed in late 2013 on an array of charges, including treason and corruption.

South Korea and the United States said Tuesday they would kick off their annual joint military exercises on March 2, setting the stage for a likely surge in tensions with North Korea.

Pyongyang had offered a moratorium on nuclear testing if this year's joint drills were cancelled -- a proposal rejected by Washington as an "implicit threat" to carry out a fourth nuclear test.

North Korea has banned foreigners taking part in its annual international Pyongyang marathon in April because of continuing concerns over the spread of the deadly Ebola virus, specialist tour groups said Monday.

China-based agencies, Koryo Tours and Young Pioneer Tours, both said they had been informed of the decision on Monday morning.

North Korean leader Kim Jong-Un has urged the army to ensure its combat readiness ahead of U.S.-South Korea military exercises that see an annual spike in tensions on the divided peninsula.

In a "historic" speech to the ruling party's Central Military Commission (CMC), Kim said the army had to be "fully ready to react to any form of war to be ignited by the enemy," state media said Monday.

North Korea's leader Kim Jong-Un has guided a military drill simulating an attack and seizure of a frontline South Korean island, Pyongyang's state media said Saturday.

The drill came as tensions grow ahead of an annual U.S.-South Korea joint Key Resolve/Foal Eagle military exercise that is reportedly to start early next month.

The head of a U.N. inquiry into rights violations in North Korea said Tuesday that Pyongyang's actions, while constituting a crime against humanity, fell short of genocide.

Michael Kirby, the Australian former judge who headed the U.N. Commission of Inquiry into North Korea's human rights violations that concluded last year, reiterated the panel's finding that "crimes against humanity have been committed" by the North Korean government in its mistreatment of thousands of prison detainees.