The United States is considering how to address this threat, coinciding with mounting speculation that Pyongyang may hold a test on Saturday, the source said.
"They are already studying military options," he said on condition of anonymity. "With this government, it is not a question of whether it will occur, but rather when."
In the last few hours, information about a nuclear activity in North Korea has been scheduled for Saturday, the day of celebrating the 105th anniversary of Kim Il-sung.
"They just wired, it's no surprise because the anniversary is on Saturday, traditionally [North Korean leader Kim Jong-un] organizes a big parade and takes their weapons and imitation weapons," said the adviser.
"Unfortunately it is not a surprise to us, [Kim] continues to develop his program, continues to launch missiles into the Sea of Japan. With the regime is not a question of whether it will occur, but when."
President Donald Trump has already said that his administration will take on the "problem" that North Korea supposes.
More complicatedThese revelations are made shortly after the US military launched on Thursday "the mother of all bombs", its most potent non-nuclear device, against a complex of the extremist Islamic State (EI) group in Afghanistan.
Trump also showed his military strength last week by bombing a Syrian government airbase with missiles, which he accused of executing the alleged chemical attack on a rebel city that left nearly 100 dead.
In addition, the agent has ordered the shipment of an aircraft carrier and its fleet to the Korean peninsula.
Trump has always said he would prevent Pyongyang from obtaining nuclear-capable ballistic missiles that could reach US territory.
When he met with Barack Obama shortly after winning the presidential elections, he was warned that he might have to make a complicated decision on this issue early in his term.
As a result, Trump asked his advisers a range of options for tackling North Korea's nuclear program.
But the White House knows that attacking North Korea is "much more complicated" than attacking Syria, according to another official source.
Any bombing of Pyongyang could trigger reprisals against Washington allies or US forces sent to South Korea and Japan.
However, the Trump administration has good diplomatic and economic options to manage this issue.
Pyongyang already suffers from various sanctions imposed by the United Nations for its nuclear and ballistic programs.
In an interview with The Wall Street Journal, Trump explained that his Chinese counterpart Xi Jinping has removed from his mind the idea that Beijing will force North Korea to change course.
"After listening for 10 minutes, I realized that it is not so easy," he acknowledged.
"I realized that [Beijing] has a lot of power" over North Korea, "but not in the way anyone can imagine," he said.
Trump will send his vice president, Mike Pence, to Asia on Saturday to visit his allies.
Pence will go to South Korea, Japan, Indonesia and Australia. At every meeting, Pyongyang will dominate its agenda.
Except for Indonesia, the United States has a treaty that obliges it to defend these countries, an obligation already questioned by the president.
Mike Pence will try to convince his allies that this commitment is "invulnerable," according to the White House counsel.
"We are fully committed to our security alliances, especially in the face of the challenges of our changing security, such as the nuclear threat that North Korea assumes," he said.