This undated picture released by North Korea's Korean Central News Agency (KCNA) on May 22 shows leader Kim Jong Un, center, inspecting the test-fire of a ground-to-ground medium-to-long range strategic ballistic missile.
South Korea says it has fired warning shots at an object that flew across the demilitarised zone from North Korea.
A statement by South Korea's joint chiefs of staff claimed the military first broadcast a warning to North Korea about the object, before it fired any shots. North Korea has accused the USA of escalating tensions with its actions and refers to its missile launches as measures to safeguard its country.
The US and South Korea, which hosts 28,500 US troops, have said the deployment is aimed purely at defence against the North Korean threat.
South Korean activists regularly send propaganda balloons into North Korea, carrying leaflets or videos. The missile was launched in Pukchang, which is just northeast of the capital, Pyongyang, and was said to have flown for 310 miles before landing somewhere on North Korea's east coast.
The latest warning shots against the DPRK projectile was sacked in January previous year when a DPRK UAV crossed the military demarcation line in the western border.
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Although North Korea has made a show of force for new USA leaders in the past, the threat is higher now because of North Korea's expanding nuclear capabilities.
The object had not been identified and its radar course was being investigated, the military said in a statement.
According to 38 North, the US-Korea Institute at John Hopkins SAIS, if Kim Jong-un can launch his missiles from anywhere, it would be extremely hard for countries like Japan, China, and the United States to target launch positions with air strikes.
The UN Security Council on Monday vowed to push all countries to tighten sanctions against North Korea as it prepared for a closed-door meeting called in response to the latest missile launch.
The UN initiative favoured by Moscow and Beijing would also put further pressure on North Korea to stop its missile and nuclear testing.
The North has made no secret of its plans to develop a missile capable of striking the United States and has ignored calls to halt its weapons programs, even from China.
The border incident came two days after Pyongyang fired a ballistic missile into the Sea of Japan.