North Korean leader Kim Jong Un placed his military on high alertand declared a "quasi-state of war"in areas near the country's border with South Korea Friday.The action took place after North and South Koreaexchanged artillery fire near the border.The Korean Central News Agency reported that Mr. Kim saidfrontline groups would "enter a wartime state"starting at 5:00 p.m. local time Friday.North Korea has made similar declarations in 2010 and 2013.The two Koreas are technically at war.The truce that ended the Korean Warin the 1950s did not become a peace treaty.Tensions increased Thursday when North Korea fired artilleryat South Korean military positions along the western border.The South responded by launching artillery rounds at the North.The artillery shells appeared to have fallen into the demilitarized zone,or DMZ, separating the two Koreas.Neither side reported damage or injuries.North Korea's ambassador to China Ji Jae Ryongspoke to reporters late Friday in Beijing.He said "If the enemy ignores our warningit is inevitable that there will be action.Our army does not use empty words."North-South relations became strained after South Koreaaccused the North of planting landmines that exploded this month near the border.Two South Korean soldiers were wounded.South Korea answered by restarting anti-North Korean broadcasts on loudspeakers near the border.The North warned Thursday that it would take further military actionif South Korea did not stop the broadcasts within 48 hours.South Korean officials have said the broadcasts would continue.And it has raised its military readiness alert to its highest levelto indicate immediate danger, imminent attack or invasion.Korea expert Daniel Pinkston is with the International Crisis Group in Seoul.He says neither side feels it can back down but neither side wants war either."I think that both sides want to avoid a high intensity conflictbut nevertheless there's a possibility of miscalculation and inadvertent escalation."The United States Thursday said it was watching the situation closely.State Department spokesman John Kirby saidthat "provocative actions" by the North only heighten tensions.He urged North Korea to refrain from actions and rhetoricthat threaten peace and security in the area.The latest tension also comes during annual joint military exercises that began Monday.North Korea condemns them as preparation for war.The exercises include South Korea, the U.S. and other allies including Britain, Canada and Australia.Daniel Pinkston says having the multinational military presence on the Korean Peninsulamight keep North Korea from actingbut may also restrain South Korea.