North Korea fired two ballistic missiles off in a northeastern direction Monday, South Korea's military said, after warning of countermeasures against a joint military exercise held by South Korea, the United States and Japan. The Joint Chiefs of Staff (JCS) said one short-range ballistic missile was launched from the Jangyon area in South Hwanghae Province at about 5:05 a.m. and flew about 600 kilometers. Another ballistic missile was launched at around 5:15 a.m. and flew about 120 kilometers. North Korea last launched two short-range ballistic missiles from the Jangyon area in March last year. The JCS strongly denounced the latest launch as a "provocative act" that gravely threatens peace and stability on the Korean Peninsula, and vowed to maintain overwhelming readiness against such provocations. "While strengthening our monitoring and vigilance against additional launches, our military is maintaining a full-readiness posture while sharing North Korean ballistic missile data with U.S. and Japanese au thorities," the JCS said in a text message sent to reporters. On Sunday, the North's foreign ministry denounced the three-day multi-domain "Freedom Edge" exercise, saying the country would take "offensive and overwhelming" countermeasures against what it called an attempt to strengthen a military bloc. The drills, which ended Saturday, involved fighter jets and warships, including a U.S. aircraft carrier. The latest launch came five days after the North's firing of a ballistic missile toward the East Sea on Wednesday. The North claimed the next day to have successfully conducted a multiple warhead missile test, but the South has dismissed the claim as "deception," saying the launch ended in failure as the missile exploded in midair. North Korea has ratcheted up cross-border tensions in recent weeks, launching trash-carrying balloons to South Korea in a tit-for-tat move against anti-Pyongyang leaflets sent by North Korean defectors and activists in the South. The latest launch also took place amid growin g concerns over deepening military cooperation between Pyongyang and Moscow after North Korean leader Kim Jong-un and Russian President Vladimir Putin signed a "comprehensive strategic partnership" treaty during a summit last month in Pyongyang. The pact includes a pledge for the two countries to come to each other's aid if attacked. Source: Yonhap News Agency