The missile launches come as tens of thousands of South Korean and US troops take part in joint military drills in the South, which Pyongyang views as a highly provocative rehearsal for an invasion of its own territory.
White House press secretary Sarah Sanders said US President Donald Trump was aware of the launches.
“In regards to activity in North Korea tonight, the president has been briefed and we are monitoring the situation,” she said.
The launches came as North Korea state media reported that leader Kim Jong-Un oversaw a military exercise simulating a special forces assault on South Korean border islands involving aircraft, “multiple-missile launchers” and howitzers.
The North tends to carry out test-firing of missiles or other projectiles — including those from long-range multiple rocket launchers — in response to the US-South Korea joint military exercises.
In recent weeks the North has threatened to fire a salvo of missiles toward the US Pacific territory of Guam, but has since backed away from the plan and tensions have eased.
Under Kim, Pyongyang has made rapid strides in its ballistic missile technology, which it is banned from pursuing under United Nations resolutions that have slapped it with seven sets of sanctions.
Last month it carried out two successful ICBM launches, overseen by Kim and apparently bringing most of its sworn enemy the United States into range for the first time.
History of two Koreas
Division of Korean Peninsula into North and South Korea was done after the victory of allies in World War II in 1945. However, when North Korea invaded South in 1950, Korean War started which continued for 3 years.
After the end of the war, both Koreas are divided by 4km wide demilitarized zone as per the agreement which took place in 1953.
However, since then both Koreas are increasing their military capabilities by spending more on their armies and weapon developments. South Korea is backed by the US whereas North Korea is allegedly backed by China.
North Korea spends the highest percentage of GDP on the military than any other country in the world.
Reach of missiles developed by North Korea
Despite many sanctions from UN, North Korea continues to test several ballistic missiles. These tests also forced the US and its regional allies, South Korea and Japan to impose sanctions on North Korea.
The US fears that North Korea can use missiles to deliver a nuclear payload to its west coast. However, it is not clear whether North Korea is able to do so.
Trading partner of North Korea
Main trading partner of North Korea is China. Over 80% of its trade is done with the People’s Republic of China. It may be noted that China is one of the few countries friendly to North Korea.