Tokyo - Japan's defence ministry on Wednesday deployed three T4 training planes to collect possible radioactive material in the air following North Korea's claimed hydrogen bomb test, officials said.
"To understand the impact of possible radioactive materials released by the test, Air Self-Defence Force planes have collected dust in the air," said chief cabinet secretary Yoshihide Suga, the government's top spokesperson.
"It is currently being sent to the Japan chemical analysis centre," he said.
Suga added that the planes flew in Japanese airspace, while the Sankei Shimbun daily reported that the aircraft took off from three separate bases in different parts of the country.
The cabinet secretary also said no abnormal levels of radiation had so far been detected through monitoring posts installed across Japan.
The results collected by the planes are expected to be released on Thursday, an official with Japan's Nuclear Regulation Authority told reporters.
North Korea's test, which came just two days before leader Kim Jong-Un's birthday, was initially detected by international seismology monitors as a 5.1-magnitude tremor next to the North's main Punggye-ri nuclear test site in the northeast of the country.
North Korean leader Kim Jong-Un last month suggested Pyongyang had already developed a hydrogen bomb, though the claim was questioned by international experts and there was continued scepticism over Wednesday's announcement.
Russia on Wednesday slammed the claimed testing of a hydrogen bomb by North Korea as a clear breach of international law that could enflame tensions across the region.
"If this test is confirmed then it will be a new step by Pyongyang on the path of developing nuclear weapons, which is a flagrant violation of international law and existing UN Security Council resolutions," Russia's foreign ministry said in a statement.
Meanwhile in Brussels the European Union condemned North Korea's claimed hydrogen bomb test as a "grave violation" of a UN ban on its development of nuclear weapons and a threat to the region.
EU foreign affairs head Federica Mogherini said: "If confirmed, this action would represent a grave violation of (North Korea's) international obligations not to produce or test nuclear weapons, as determined by several United Nations Security Council Resolutions and a threat to the peace and security of the entire northeast Asia region."