The missile launches come as tens of thousands of South Korean and USA 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.
Benham says the military continues with a more detailed assessment.
The launches were spread over a period of 30 minutes, an official said.
They are the first known missile firings since July, when the North successfully flight tested a pair of intercontinental ballistic missiles that analysts say could reach deep into the U.S. mainland when perfected.
South Korea's presidential office and military said North Korea fired "several" projectiles in what was presumed as a test of its 300-millimeter rocket artillery system.
Pyongyang responded by saying it was working on a plan to launch a medium-range ballistic missile close to the U.S. territory of Guam, some 3,200km from North Korea.
The missiles reportedly landed in North Korean waters about 250km away. The US ban on American citizens traveling to North Korea takes effect September 1.
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Heightening concerns about North Korea's aims, state media last week reported that leader Kim Jong Un visited the Chemical Material Institute of the Academy of Defence Sciences and inspected designs for two new long-range missiles.
The country's chief cabinet secretary announced Japan intends to freeze assets of six more North Korean organizations as well as two individuals with ties to Pyongyang and Beijing.
"We hope that this is the beginning of this signal that we've been looking for - that they are ready to restrain their level of tensions, they're ready to restrain their provocative acts and that perhaps we are seeing our pathway to sometime in the near future having some dialogue", Tillerson said.
Analysts said the photos were a sign from North Korea to the world, to show their solid fuel missile program is improving at a steady rate.
The situation on the Korean peninsula has become aggravated in recent months due to a series of missile launches and nuclear tests conducted by Pyongyang in violation of UN Security Council resolutions.
The rival Koreas recently saw their always testy relationship get worse after Mr Trump traded warlike threats.
U.S. Army soldiers prepare for their military exercise in Paju, South Korea, near the border with North Korea, Saturday, Aug. 26, 2017.