Earlier in the day, he visited a USA base near the Demilitarized Zone dividing the two Koreas. Apparently sensing a worsening political environment, the US military sped up the deployment to try to get everything in place before the election.
The spokesman's remarks followed North Korea's latest missile launch provocation. Whatever China's doubts, the missile strike against Assad displayed in dramatic fashion that Trump is willing to intervene suddenly in situations that others believe to be frozen and immune to intervention.
McMaster was speaking hours after USA and South Korean defense officials told CNN that an attempted missile launch by North Korea failed.
South Korea said it would convene a national security council meeting on Sunday.
He said: "We would sneak into the South, change our clothing, go into areas where there are lots of foreigners and capture some of them".
Pence told reporters near the DMZ that President Donald Trump was hopeful that China would use its "extraordinary levers" to pressure the North to abandon its weapons program, a day after the North's failed missile launch.
H R McMaster indicated that Mr Trump was not considering military action for now, even as a nuclear-powered aircraft carrier strike group was heading for the region.
The U.S. vice president, however, said "all options are on the table" though the U.S. wants peaceful means for the denuclearization of the peninsula.
"There is an global consensus now, including the Chinese leadership, that this is a situation that just can not continue".
Any U.S. military strike risks leading to a war that may devastate South Korea and Japan, two American allies in striking range of retaliatory attacks.
Congressman Mac Thornberry, McCain's counterpart in the House of Representatives, said Kim's message to the United States was "we are strong and we can hurt you". Sitting tight will eventually put the American heartland within range of North Korean nuclear missiles, raising the prospect that Pyongyang will see U.S. nuclear deterrence as checked. His visit came a day after North Korea held a military parade in its capital, Pyongyang, marking the 105th anniversary of the birth of founding father Kim Il Sung.
Wearing a Western-style black suit and white collared shirt, Kim was pictured on state-run television laughing heartily and clapping while watching soldiers, tanks and missiles on display in a large square.
Pence is noting in a statement alongside South Korean Acting President Hwang Kyo-ahn that President Donald Trump recently launched airstrikes in Syria.
On Friday, North Korea said the risky security situation was due to the "Trump administration's reckless military provocation".
McMaster repeatedly stated that China - North Korea s key ally - is increasingly concerned about the reclusive communist state s behavior.
This year we were expecting to see a new missile, but what we got was something of a scale never seen before.
"Not only did they establish a very warm relationship, but since that time, they've worked together on other issues", McMaster said, referring to Trump and Xi.
North Korea has displayed the KN-08 missiles three times since 2012, and unveiled the KN-14, a new variant, in 2015.
On Thursday, the U.S. military said it had dropped "the mother of all bombs", the largest non-nuclear device it has ever unleashed in combat, on a network of caves and tunnels used by Islamic State in eastern Afghanistan.
Japanese Prime Minister Shinzo Abe has urged North Korea to refrain from taking further provocative actions, comply with United Nations resolutions and abandon its nuclear missile development.
Japan's Prime Minister Shinzo Abe has reiterated that pressure, not only dialogue, is necessary in dealing with North Korea's missile and nuclear threat.
"We weren't surprised by it, we were anticipating it", the foreign policy adviser said.