North Korea on Monday again threatened to launch nuclear strikes on the United States and South Korea, as the two countries started their annual joint military drills. The U.S. and South Korea began their biggest-ever joint exercise Monday, involving 300,000 South Korean and 17,000 U.S. troops. The drills, which the North claims are preparations for war against it, will continue until the end of April The North said its enemies "are working with bloodshot eyes to infringe upon the dignity, sovereignty and vital rights" of the country in a statement carried by the official Korean Central News Agency. A woman cycles with her child riding in a basket in Kaesong on Feb. 22, 2016. Wong Maye-E, AP USA TODAY North Korean leader wants nukes ready to fly "The army and people of the (North) will take military counteraction for preemptive attack so that they may deal merciless deadly blows at the enemies," the North’sNational Defense Commission said. "If we push the buttons to annihilate the enemies even right now, all bases of provocations will be reduced to seas in flames and ashes in a moment,” it added. South Korean Defense Ministry spokesman Moon Sang Gyun told reporters: "If North Korea launches a provocation, our military will respond sternly and mercilessly." USA TODAY Marines arrive for drills in Korea amid North’s threats USA TODAY S. Korea: North fires projectiles into sea hours after U.N. Security Council approves sanctions Last week, the South Korean Defense Ministry said the North fired several short-range projectiles into the sea, hours after the U.N. Security Council approved the toughest sanctions in decades against the North in response to its recent nuclear and missile tests. The North's leader Kim Jong-Un ordered nuclear weapons to be readied for use, the Korean Central News Agency reported. North Korea conducted its fourth nuclear weapons test in January, claiming it tested a hydrogen bomb, and fired a long-range rocket over Japanese airspace on Feb. 7 in what was widely condemned as a test of missile technology banned by previous U.N. resolutions.