North Korea announced Thursday that what they had fired the day before was its "Hwasong-17" ICBM.
But the South Korea military is said to be leaving open the possibility that it was actually a different type of ICBM possibly the "Hwasong-15" that the North launched in 2017.
"The South Korea and U.S. intelligence agencies are currently conducting detailed analysis, with a variety of possibilities in mind."
North Korea's Hwasong-15 and Hwasong-17 are both ICBMs, but experts say the large size of the Hwasong-17 suggests that the North is aiming to tip it with multiple nuclear warheads.
The Hwasong-15 is estimated to be around 21 meters in length and 2 meters in diameter.
The Hwasong-17 is slightly longer at around 24 meters and 2.4 meters in diameter.
Analysts say this makes Hwasong-17 the largest liquid-fueled ICBM in the world.
One expert says even if it was the Hwasong-15, the North seems to have developed it into a much more advanced version.
"Because the North failed its launch on March 16th, it's logical to be suspicious about the regime suddenly recording a huge success just eight days later. But, looking at the range, altitude, and speed, even if it is a Hwasong-15, it's true that it's a much more developed version."
North Korea had last launched the Hwasong-15 in November 2017.
It flew 950 kilometers, at a maximum altitude of around 4,500 kilometers.
The missile on Thursday flew more than one-thousand kilometers at an altitude of around 6,200 kilometers much higher than four years ago.
Another expert says there is no reason for the North to lie,.. because if it has the capability to launch a Hwasong-15 this far, it could have done so in 2017 as well.
"I mean they could think that it's possible for it to be the Hwasong-15, because the North failed to launch Hwasong-17 but I don't think there is any reason for North Korea to fabricate things."
Bae Eun-ji, Arirang News.