North Korean leader Kim Jong-un has pledged to “crush” the hostile policy of the U.S., lambasting its ongoing military drills with South Korea that Pyongyang claims are heightening tension on the peninsula, state media said Wednesday.

The current political situation is “extremely grave,” he said, despite a series of measures he has taken since early this year to “bring about a turning point for the improvement of inter-Korean relations and unification.”

“The U.S. and its hostile allies are unscrupulously conspiring to politically wipe out, economically isolate and militarily choke off our republic in disregard of our generosity and good faith,” Kim was quoted as saying by state media at a rally of military commanders in the northeast province of Ryanggang on Tuesday.

“Our military and people will never accept and will thoroughly batter the U.S.’ hostile anti-North Korea policy.”

The young leader’s rare verbal address, his third this year, came as tension escalates on the peninsula amid military exercises on both sides of the border and Pyongyang’s threats of a fourth nuclear test.

Key military officials attended the event, including Choe Ryong-hae, director of the Korean People’s Army’s General Political Bureau; Jang Jong-nam, minister of the People’s Armed Forces; and Pyon In-son, director of the KPA’s General Staff Operations Bureau.

The two Koreas on Monday briefly traded fire across the Northern Limit Line after the North dropped about 100 artillery shells south of the de facto sea border during its live-fire drills in the West Sea. The South, which has been staging a series of military drills with the U.S. since late February, shortly fired back some 300 shots with its K-9 self-propelled howitzers.

The communist state said on Sunday it will not rule out a “new type of nuclear test” to further beef up its nuclear deterrence in protest against the U.N. Security Council’s condemnation of its ballistic missile tests last week.

The moves contrasted Pyongyang’s peace offensive early this year, which intensified after Kim called for the improvement of inter-Korean ties as a key national task in his New Year address. The two sides held the first reunion of families separated by the Korean War in more than three years in February and have made progress on a joint factory park in the North’s border city of Gaeseong.

The turnaround appears to reflect the Kim regime’s displeasure with the joint military exercises and Seoul’s North Korea policy. The North’s official media on Tuesday denounced President Park Geun-hye’s proposal last week for broader cross-border exchanges such as through the establishment of inter-Korean cooperative offices and greater humanitarian, financial and infrastructure support.

Beijing, the main supporter of Pyongyang, has expressed concerns over further tension, urging all sides to work to maintain peace and stability in the region.

The international community is stepping up calls on China to dissuade its wayward ally from another underground detonation.

Daniel Russel, U.S. assistant secretary of state for East Asian and Pacific affairs, said Beijing is struggling to balance “two contradictory imperatives” in its North Korea policy -- stability and denuclearization.

“One is the maintenance of stability on its border,” he said in a conference call hosted by the Asia Society in Washington. “The other is ending North Korea’s quest for nuclear weapons capability.”

Seoul’s ambassador to China Kwon Young-se said Wednesday that relations between Pyongyang and Beijing appear to be “less smooth than in the past” in the wake of the North’s third nuclear test and the execution of Kim’s powerful uncle, Jang Song-thaek, though they have restored some high-level exchanges.

“The Chinese side is closely monitoring, with concerns whether there will be another nuclear test,” Kwon told reporters. “But there appeared to be no signs of something imminent.”

By Shin Hyon-hee (heeshin@heraldcorp.com)