North Korea has launched two ballistic missiles, the South Korean military said on Monday, as Pyongyang warned of countermeasures against a joint military drill.

The missiles were launched from South Hwanghae Province, South Korean news agency Yonhap reported, citing the authorities in Seoul. It said that one missile had flown about 600 kilometers (372 miles) while the second flew about 120 kilometers.

"The South Korean military will maintain its capacity and posture to respond overwhelmingly to any provocation while closely monitoring North Korea's various activities under a strong South Korea-US joint defense posture," a military spokesperson said in a press conference.

Pyongyang's state-controlled KCNA news agency spoke of a successful test for a "new important technology."

However, a spokesman for the South Korea Joint Chiefs of Staff told journalists that one of the test missiles had exploded in the early phase of the flight.

Seoul was still analyzing the launch and did not immediately have confirmation whether there were any casualties or damage to North Korean property, the spokesperson said.

North Korea slams 'Asian NATO'

The launch comes less than a day after North Korea criticized a joint military exercise by South Korea, Japan and the United States held this month, calling the alliance "the Asian version of NATO."

North Korea would "firmly defend the sovereignty, security and interests of the state and peace in the region through offensive and overwhelming countermeasures," a statement carried by Pyongyang's state-controlled KCNA news agency had said.

Under the rule of its supreme leader, Kim Jong Un, North Korea has developed nuclear-capable missiles in recent years, despite international sanctions against Pyongyang over its nuclear weapons and missile program.

South Korean officials have previously said North Korea's recent short-range ballistic missile launches may be intended to show its wares to potential buyers.

North Korea is suspected of supplying ballistic missiles and artillery shells to Russia — an allegation both countries deny despite their pledges of military cooperation and a pact of mutual military support.