The hi-tech aircraft sniffers, technically referred to as WC-135, will be used to detect nuclear radiation levels in the hermit kingdom.
According to a Japanese newspaper, the aircrafts have been flying over North Korea since 2006.
Donald Trump has deployed nuclear 'sniffers' in Japan to observe North Korea's activity
The pictures Kim Jong-un WANTS you to see of inside North Korea
Wed, April 12, 2017
Fascinating photographs depict life inside North Korea as Kim Jong-Un wants you to believe
1 of 18
A North Korean student swings on a bar in a school in Pyongyang, North Korea
A snippet of the report said: “Since 2006, when Pyongyang detonated an underground nuclear device, Washington has been deploying its two WC-135 aircraft to the region — planes which also flew over the Fukushima Dai-ichi nuclear power plant after its meltdown in 2011.”
Details of their nuclear observations follow announcements that the the US and Japan will launch joint military drills to threaten Kim Jong-un.
Reports have said, the Japanese Maritime Self Defence Force (MSDF) may carry out helicopter landings on the USS Carl Vinson, which was deployed near the Korean peninsula in the wake of Kim Jong-un’s missile tests.
Get Quotes on Home Insurance
It is believed the joint military drills are to be carried out as a show of strength towards Kim Jong-un’s despotic regime.
A North Korean Foreign Ministry spokesman slammed Mr Trump’s move. Speaking to the Korean Central News Agency, the spokesman said: “This goes to prove that the US reckless moves for invading the DPRK have reached a serious phase.
Shinzo Abe, Japanese PM is working with Trump against North Korea
“If the US dares opt for a military action, crying out for 'preemptive attack' and 'removal of the headquarters' the DPRK is ready to react to any mode of war desired by the US."
Officials have predicted, Jong-un may launch a nuclear strike to commemorate Kim Il-sung’s birthday, called "The Day of The Sun" in Pyongyang – celebrated on April 25.
With growing tensions, the Korean peninsula is the closest it has been to a "military clash" since Pyongyang's first nuclear test in 2006, an influential state-run Chinese newspaper said.