North Korea is conducting military exercises, similar to those by South Korea, amid the recent heightening of tensions in the peninsula, South Korea's Yonhap News Agency reported Tuesday. North Korea’s exercises are aimed at key public facilities in Seoul and are part of what it calls an “operation to liberate Seoul,” a South Korean lawmaker reportedly said, citing government officials.

The news follows the joint military exercises by the U.S. and South Korea on the latter's beaches in the eastern coastal city of Pohang. They are part of the two countries' largest ever joint military exercises — Key Resolve and Foal Eagle — that began last week. The drills triggered threats of attacks from Pyongyang Saturday.

The South Korean lawmaker also said that North Korea could conduct military provocation on the Korean border and send drones to the South as part of its exercise. He added that the Kim Jong Un regime could conduct terrorist attacks in Seoul and other nearby areas, launch missiles or jam GPS networks.

“The [South Korean] military is having preparatory training against the possibilities,” the lawmaker reportedly said.

Earlier Tuesday, the North Korean official news agency KCNA said citing Kim Jong Un that the country had successfully tested a nuclear warhead re-entry in a lab and would soon conduct a nuclear warhead test and test launch ballistic missiles capable of carrying nuclear warheads.

KCNA said that Kim made the comments as he supervised a test for the atmospheric re-entry of a ballistic missile, which measured the “thermodynamic structural stability of newly developed heat-resisting materials.” The test reportedly gave a “sure guarantee for the reliability of the intercontinental ballistic missile warhead re-entry.” Seoul is currently verifying if North Korea will go ahead with the threat.

Skepticism follows North Korea’s latest claim of mastering the re-entry technology and its earlier claims of successfully miniaturizing weapons, but if true, it would allow Pyongyang to fire nuclear-tipped intercontinental ballistic missiles that can target the U.S. 

“Seoul believes that the North has yet to secure such technology,” a South Korean military official said, according to Yonhap earlier Tuesday, adding: “North Korea's claim is seen as aiming to flex its military muscles.”

Worries in the region have amplified over the past few weeks as Pyongyang has conducted a nuclear test, launched rockets and test-fired several missiles. The reclusive country's aggressive moves have drawn sanctions from the United Nations Security Council that also bans export of jet fuel into North Korea. Seoul is currently investigating how North Korea is able to procure aviation fuel for the tests despite the sanctions.

“North Korea may push ahead with another nuclear test by detonating a stronger fission bomb before it holds its key party congress in May,” Cheong Seong-chang, a senior researcher at the South Korean think tank Sejong Institute, said, according to Yonhap.