North Korea on Tuesday strongly denounced the upcoming joint military exercise between Seoul and Washington, warning a "pre-emptive strike" against any attempt to collapse the Kim Jong-un regime.

South Korea and the United States plan to conduct their largest-ever military drill next month at a time of heightened tension on the Korean Peninsula following Pyongyang's recent nuclear test and long-range missile launch.

In response, the North Korean military said it will use all possible measures to counter any attempts to decapitate its leader and collapse its regime, calling the planned joint drill "the height of hostile acts."

We "are ready to immediately and mercilessly punish without slightest leniency, tolerance and patience anyone provoking the dignified supreme headquarters even a bit," the Supreme Command of the Korean People's Army said in an English statement carried by the Korean Central News Agency.

The first subject is South's presidential office, the commander said, threatening to strike U.S. forces in Asia-Pacific region and the mainland as the next targets.

The two allies have carried out annual joint exercises -- Key Resolve and Foal Eagle -- since the 1990s to better deter North Korean aggression. The North claims the drills are a rehearsal for a northward invasion.

This year, the drills will likely involve about 15,000 American soldiers and increased military assets, about twice the size of the exercise conducted last year, the defense ministry said earlier.

The stronger reaction comes as the U.S. military has sent high-profile military assets to the peninsula over the past weeks in a show of force against its provocations.

Pyongyang conducted its fourth nuclear test on Jan. 6 and launched a long-range rocket on Feb. 7, which the outside world denounced as a test of ballistic missile technology banned by international sanctions.

Days after the nuke test, a U.S. B-52 bomber flew over South Korea as the allies took to deterring North Korea from further escalating military tensions, which were followed by four F-22 stealth bombers and a nuclear-power submarine.

Seoul defense officials took the North's strong words as a sign of uneasiness over the recent exercises conducted with American militaries, vowing to maintain a tight readiness to counter any provocations.

Kim Yong-hyun, a professor of North Korean studies at Dongguk University, said the warning is part of its "psychological warfare" tactics because its goal to strike the presidential office seems unrealistic.

"(The statement) shows that North Korea is uncomfortable with the meer idea of an operation targeting its ruler," Kim said.

Relations between two Koreas have fallen to all-time low as President Park Geun-hye earlier this month shut down a joint industrial park just north of the Demilitarized Zone and resumed cross-border propaganda broadcasts critical of Kim Jong-un.

Seoul has also been negotiating with Washington to deploy the Terminal High Altitude Area Defense, a high-tech U.S. missile defense system, on the peninsula, which drew strong backlash from Beijing.

Source: Yonhap news agency