North Korea has lambasted the ongoing joint military exercises by South Korea and the United States with fiery rhetoric, warning of “merciless nuclear counter-action” in case of military aggression by the two countries.

“Now that the US imperialists and the south Korean puppet forces again kicked off the dangerous nuclear war drills against the DPRK [the Democratic People’s Republic of Korea] at its doorstep, our army will counter them with the toughest counter-actions as it had already declared,” North Korea’s official KCNA cited a statement by an unidentified military spokesman as saying on Thursday.

The North’s strong reaction came a day after the war games began in the region. Some 15,000 US and 90,000 South Korean troops are expected to participate in the two-phased joint exercises, known as Key Resolve and Foal Eagle, which will stretch over two months.

A group of demonstrators convened outside the US Embassy in Seoul on Wednesday to protest the drills, saying the exercises would push the Korean Peninsula closer to the brink of a nuclear war.

South Korean anti-war activists hold placards showing a caricature of US President Donald Trump during a rally against the South Korea-US joint military exercises, near the US Embassy, in Seoul, March 1, 2017. (Photo by AFP)

Seoul and its key ally Washington hold the annual joint military exercises as a signal to Pyongyang, which has been rapidly developing a missile and nuclear program. The North, however, perceives the maneuvers as a direct threat against its security and planned rehearsals for an invasion on its territory.

The US currently has 28,500 troops stationed in South Korea as a presumed deterrent force against North Korea.

“The forces of vassal countries will be targets of our strikes as they are imprudently involved in the ongoing saber-rattling, toeing the US imperialists’ hostile policy toward the DPRK,” the North Korean statement further warned.

The United Nations (UN) and the European Union (EU) have already imposed an array of crippling sanctions on the North over its nuclear tests and missiles launches. On Monday, the EU also imposed additional sanctions on the country. The fresh measures included restrictions on trade in coal, iron, and iron ore, plus a ban on imports of copper, nickel, silver, and zinc from North Korea.

This photo, released on February 13, 2017 by North Korea’s KCNA, shows the launch of a Pukguksong-2 ballistic missile. (Via Reuters)

Despite the sanctions and other forms of international pressure, Pyongyang declared itself a nuclear power in 2005 and has pledged to strengthen its military capability to protect itself from the threat posed by the presence of the US forces in the region.

North Korean leader Kim Jong-un also accuses the US of plotting with regional allies to topple his government.

Pyongyang said on February 13 that it had successfully test-fired a new type of medium- to long-range ballistic missile the previous day, its first such test in 2017. The missile reportedly flew about 500 kilometers toward Japan, landing off the east coast of the Korean Peninsula.