USA intelligence officials has been continuously montoring the North Korean submarine movements and detected that Sang-O submarine was operating in the Yellow Sea and the length of its deployment was notable.
American student Otto Warmbier, sentenced last year to 15 years' hard labour in North Korea, returned to the United States in a coma on June 13 after being released on humanitarian grounds, and died June 19.
An ejection test examines a missile's "cold-launch system", which uses high pressure steam to propel a missile out of the launch canister into the air before its engines ignite.
A ban on travel by U.S. passport holders to North Korea will take effect on September 1 and Americans in the country should leave before that date, the U.S. State Department said on Wednesday.
According to a 2012 bilateral missile treaty between Washington and Seoul, however, South Korea must first gain permission from the United States before it can increase its arsenal, cited by the New York Times.
Though he has at times sought a more conciliatory approach, Trump also has lambasted China over such problems and over the massive USA trade deficit.
"It sends the message to the North Korean dictator that the global community is unwilling to seriously challenge him".
Tillerson is travelling to Asia this week, where he will continue his drive to increase "peaceful pressure on the regime in North Korea to have them develop a willingness to sit and talk to us and others". I believe him. If I were China, I would believe him, too, and do something about it.
"It seems to be a predictable pattern where the North provokes, South Korea gets angry, and then time passes and the forces for a softer approach reassert themselves", said Newsham. "China could easily solve this problem!"
"There is no future where North Korea holds nuclear weapons or the ability to deliver those nuclear weapons to anyone in the region, much less the homeland", he said.
Beijing also rejected Trump's linkage of trade and the North, with commerce vice-minister Qian Keming telling a briefing Monday the issues "are not related, and should not be discussed together".
Russia's foreign ministry, however, said it was "unjustified" for the USA and other nations to try to blame Moscow and Beijing for the situation.
McMaster has agreed, according to reports, to new talks to permit larger payloads on South Korean missiles.
South Korea's defense minister said Sunday the military will upgrade its Patriot missile system as well.
In its editorial, Xinhua said it was "definitely irrational" to blame China for North Korea's missile launch.