"The south Korean puppet forces opened warning broadcasting and fired more than 450 machine gun bullets into the DPRK side, claiming they spotted "unidentified flying objects crossing the MDL", the KPA spokesman said.
The South Korea military are as vigilant and alert as ever after North Korea did another ballistic missile test on Sunday, its 8th of the year.
The closed-door meeting on Tuesday that was requested by South Korea, the United States and Japan is known to have focused on having UN member states fully implement existing sanctions on Pyongyang.
Newly elected South Korean President Moon Jae-in is set to overhaul Seoul's foreign policy with particular emphasis on easing tensions with the North.
The Yonhap news agency and other local media speculated the object may have been a drone.
"If left on its current trajectory the regime will ultimately succeed in fielding a nuclear-armed missile capable of threatening the United States homeland", Stewart said in testimony.
In 2014, the rivals traded machine gun and rifle fire after South Korean activists released anti-North Korean propaganda balloons across the Demilitarized Zone that bisects the Korean Peninsula, but no casualties were reported.
The North's official KCNA news agency, citing the spokesman for the foreign ministry, said the country had "substantially displayed" the capabilities for mounting a nuclear attack on Hawaii and Alaska and had built full capabilities for attacking the US mainland. Despite this call, a new weekly ferry service between North Korea and Russian Federation began last week. In the past, North Korea has put fecal matter inside balloons.
Tensions have spiked on the Korean Peninsula in recent years over North Korea's missile and nuclear programs.
The United States has for weeks been negotiating a new Security Council sanctions resolution with China, but US Ambassador Nikki Haley said last week that no final draft had been clinched.
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.
North Korean leaders quite rationally concluded that Iraq's mistake was not its pursuit of a weapon but rather its failure to build one.