The vice president earlier visited a military installation near the DMZ, Camp Bonifas, for a briefing with military leaders at the joint U.S. However, the United States is in the first phase of deploying the Terminal High Altitude Area Defense anti-ballistic missile system-THAAD-in South Korea.
But as CBS News correspondent Margaret Brennan reports, Mr. Trump has refused to explain his strategy, suggesting he wants to keep the North Koreans guessing, but in an interview on Monday he said all of his predecessors had been outwitted by North Korea's ruling Kim dynasty. Is China going to cooperate with the United States of America to contain North Korea?
Mr Mattis credited China with trying to help get the North Korea situation "under control" with the goal of denuclearising the peninsula.
The North conducted two nuclear tests and 24 ballistic missile tests last year, defying six UN Security Council sanctions resolutions banning any testing, and it has launched more missiles this year including a failed attempt at the weekend.
Mattis did not identify the type of missile but said it was not of intercontinental range, meaning it could not reach USA territory.
However, US President Donald Trump chose to pull out of the deal, saying it was bad for American workers.
On April 14, US media said that US President Donald Trump might order a strike against North Korea in the event Pyongyang chose to carry out another nuclear weapon test.
The US has adopted a policy of "strategic patience" with North Korea. It test-fired a missile on Sunday that exploded within seconds of launch, following a grand military parade on Saturday.
China remains North Korea's chief source of fuel and food imports, but Pyongyang seems to have calculated that Beijing's fears of a collapse of Kim Jong Un's hard-line communist regime override any such snubs.
Meanwhile, US Vice President Mike Pence reiterated his country's commitment to guarantee the security of Japan in facing North Korea's threats.
"Just in the past two weeks, the world witnessed the strength and resolve of our new president in actions taken in Syria and Afghanistan", Pence had said, referring to missile strikes in Syria for deadly chemical attack and dropping of the mother of all bombs over IS hideout in Afghanistan.
"We'll be conducting more missile tests on a weekly, monthly, and yearly basis", NK Vice Foreign Minister Han Song-Ryol said.
Pence arrived in Tokyo on Tuesday from South Korea, where he visited the heavily fortified border separating the North and South.
But, mindful that this would likely trigger massive retaliation and casualties in South Korea and Japan, US officials say the Trump administration's main focus is on tougher economic sanctions.
The window for dialogue with North Korea should be kept open.
Trump has also decided against labeling Beijing a currency manipulator, saying it could jeopardize efforts to solve the North Korea problem. In fact, the communist country vowed to continue testing its missiles and expressed its readiness for an "all-out-war" in the event of US military aggression.
The North casts the U.S. as the aggressor.
Ms Bishop also repeated Prime Minister Malcolm Turnbull's call for China to increase diplomatic and economic pressure on North Korea.