The National Intelligence Service (NIS) told lawmakers in a closed session that Pyongyang may lob the missile around the anniversary of the regime's foundation slated for Saturday or the establishment of the ruling Workers' Party of Korea on Oct. 10.
North Korea fired ballistic missiles, including two ICBMs fired in July, at a lofted angle to prevent them from crossing over other countries including Japan. But Pyongyang lobbed a Hwasong-12 intermediate-range ballistic missile that flew over Japan last week.
"There is a possibility that the North would fire an ICBM on a standard trajectory," the NIS was quoted as saying by lawmakers.
North Korea claimed Sunday it had a successful test of an H-bomb that can be mounted on an ICBM. North Korea fired two ICBMs in July.
The NIS said that more analysis is needed to verify whether the North detonated an electromagnetic pulse-based bomb or a hydrogen bomb during its nuclear test, according to lawmakers.
"North Korea claimed an H-bomb test, but we are analyzing it on the assumption that there could be three possibilities -- a hydrogen bomb, an atomic detonation and a boosted fissile weapon," the agency was quoted as saying, source from the Yonhap.
It said that Pyongyang appeared to try to show that international sanctions are not working and to express its complaints against China or Russia by timing the detonation with a Beijing-hosted five emerging nations BRICS summit and Russia's economic forum slated for later this week.
"The North also seemed to want to spark tensions to pressure the United States into changing its North Korea policy," it added.
It said that the latest detonation was conducted in a northern tunnel of its nuclear site in the northeastern area where Pyongyang previously carried out three tests.
Since 2006, the North has conducted six nuclear tests, including two last year. The 2006 test was conducted in an eastern tunnel, which was later closed, and the fifth bomb was detonated in an auxiliary tunnel from the northern one in September 2016.
The agency said that North Korea can carry out another nuclear test at any time as it has completed the construction of the third tunnel and another one is in the final stages of completion.
It said that the second and northern tunnel is presumed to have collapsed due to the sixth test. China's quake administration said Sunday that there was another quake in the North some eight minutes after the first one due to a collapse.