South Korea successfully test-fired two long-range ballistic missiles on Wednesday in an apparent response to North Korea’s constant push to boost its nuclear and missile capabilities. According to South Korea’s defense ministry, the domestically produced missiles can strike nearly all parts of the communist North.

The missiles, which had a range of more than 300 miles, were fired from a launch pad located in the country’s south, the Associated Press (AP) reported, citing a defense ministry official, who also said that South Korean President Park Geun-hye was present at the launch.

“The successful test today allows us to deploy the new missile starting at the end of the year,” South Korea’s Yonhap news agency quoted an anonymous defense ministry official as saying.

The development of the new ballistic missiles began in 2012 when South Korea signed an agreement with the United States, which allowed Seoul to possess long-range missiles to better counter potential nuclear and missile threats from the North.

The deal also allowed Seoul to have ballistic missiles with a range of up to 500 miles. A previous 2001 agreement between Washington and Seoul had prevented the latter from deploying ballistic missiles with a range of more than 186 miles, the AP reported.

The 2012 accord also permitted South Korea to arm its ballistic missiles with warheads heavier than the current limit of 1,102 pounds, “on the condition their range decreases in proportion to the payload,” Yonhap reported.

The move comes amid growing tensions in the Korean Peninsula over Pyongyang’s recent claims that it test-fired a ballistic missile from a submarine. In response to the missile test, Seoul said it would retaliate “mercilessly.”

Last month, North Korea further heightened tensions by claiming that it has the ability to miniaturize nuclear weapons that can fit atop its long-range missiles. Although experts have questioned the authenticity of North Korea’s recent claims of conducting missile tests, they agree that the country has made serious progress in developing nuclear-tipped missile, which can target both South Korea and the U.S., the AP reported.

Admiral Harry B. Harris Jr., who assumed leadership of the U.S. Pacific Command at Pearl Harbor in Hawaii last week, said that North Korea is the biggest threat to the United States in the Pacific region, despite China’s ramped-up military presence in the South China Sea.

“The greatest threat we face is North Korea,” he said in an interview with Time magazine. “They have an unpredictable leader who is poised, in my view, to attack our allies in South Korea and Japan.”