South Korea's Defence Ministry said it was analysing exactly how the North Korean launch failed.
The visit comes after a huge military parade during which North Korea showcased apparent intercontinental ballistic missiles, and as a USA carrier group converges on the Korean peninsula, ratcheting up tensions to their highest point in years.
"All options are on the table to achieve the objectives and ensure the stability of the people of this country", he told reporters as tinny propaganda music floated across from the North Korean side.
North Korea's missiles are a particularly complicated issue in South Korea.
Vice President Mike Pence, who arrived in Seoul on Sunday, assailed the missile test as a "provocation" and assured South Korea of Washington s full support against the threat from its volatile neighbor.
At the same it's increased its military footprint in the region by deploying a naval carrier strike group to waters off the Korean Peninsula.
The official said that had it been a nuclear test "other actions would have been taken by the US".
Amid sharply heightened tensions, McMaster said the USA and allies were studying all actions "short of a military option", though the Trump administration has not ruled that out.
"We have been here before but continue to monitor the situation carefully".
In 1996 a North Korean sub landed three troops to spy on South Korea's navy near Jeongdongjin, but the vessel ran aground when it tried to collect the team.
While Trump has employed tough rhetoric in response to North Korea's recent missile tests, the president's options appear limited in dealing with a challenge that has vexed his Oval Office predecessors. At the most, to the mainland United States itself.
"The missile blew up nearly immediately", the US Defense Department said of the early morning launch which was also detected by the South Korean military.
North Korea held a large-scale military parade in Pyongyang to commemorate the 105th anniversary of the birth of North Korea's late President Kim Il Sung.
Trump wrote Sunday on Twitter that China was working with the United States on "the North Korea problem". The administration's immediate emphasis, the officials said, will be on increasing pressure on Pyongyang with the help of Beijing.More news: Angelina Jolie is getting married? Rumors and her new boyfriend
Though tensions had been rising dangerously between Washington and Pyongyang in the lead-up to the April 15 anniversary, the biggest holiday of the year in North Korea, the heightened rhetoric and saber-rattling on both sides could begin to cool down - a pattern that has been common in recent years, especially in the spring, when the USA and South Korea stage their huge annual war games.
"We will see what happens!" Trump after all tweeted less than a fortnight ago that he was prepared to act unilaterally against North Korea if it does not come to heel. Eighty percent of North Korea's trade comes from China.
The bottom line, McMaster said, is to stop the North's weapons development and make the Korean Peninsula nuclear-free: "It's clear that the president is determined not to allow this kind of capability to threaten the United States".
Pence had been briefed on the failed launch en route to Seoul and had been in touch with President Donald Trump, White House aides said.
China has openly expressed concern that fighting could erupt at any moment, Japan is talking evacuations, and Russian Federation has declared itself extremely concerned the U.S. might unilaterally attack North Korea.
"If they took the time and energy to launch a missile and fail, we don't need to expend any resources against that", the foreign policy adviser said.
"We weren't surprised by it, we were anticipating it", the foreign policy adviser said.
China has spoken out against the North's weapons tests and has supported United Nations sanctions. It has repeatedly called for talks while appearing increasingly frustrated with the North.
Had a very good call last night with the President of China concerning the menace of North Korea.
China said it cut off coal imports from North Korea in February, in accordance with U.N. Security Council sanctions.
Impoverished North Korea and the rich, democratic South are technically still at war because their 1950-53 conflict ended in a truce, not a peace treaty.
Many outside analysts believe that North Korea has not yet mastered the technology to build warheads small enough to place on long-range missiles, though some civilian experts say it can already build nuclear-tipped shorter range missiles that have South Korea and Japan within its striking range.
The North has a habit of firing off missiles to mark major political anniversaries, or as gestures of defiance to top U.S. officials visiting the region.
"And making it without prompting a furious response from Washington surely qualifies as a win to some degree from Kim's perspective", it said, referring to leader Kim Jong Un.