After the test launch last week, North Korean state media said the ballistic missile was equipped with a stable re-entry system, which allows a warhead to survive the heat-intensive process of re-entering the Earth's atmosphere.
Ballistic missiles follow an arched trajectory, whereas cruise missiles mostly travel parallel to the ground.
"Considering the fact that the missile had been launched from a fixed launcher, the NIS (National Intelligence Service) evaluates the technology is at the beginning stage," South Korean lawmaker Lee Wan-young said Tuesday.
"The NIS sees North Korea as not yet capable of re-entry technology," Lee said in a televised news conference after an intelligence briefing.
North Korea said last week it tested its first intercontinental ballistic missile, capable of reaching Alaska.
The news set off alarm bells
as the United States celebrated its Independence Day holiday and as world leaders prepared to gather for the G20 summit in Germany.
Authorities in the United States and South Korea verified the missile had intercontinental range but provided few other details.
'A matter of enough trial and error'
Acquiring a nuclear-capable ballistic missile that can hit the United States is a top priority for North Korean leader Kim Jong Un.
Pyongyang looks at leaders such as Libya's Moammar Gadhafi
, who gave up his nuclear program for sanctions relief but was eventually ousted and killed, and believes the ability to attack the United States with a nuclear weapon is the only way they can deter any American-backed attempt at regime change, analysts suggest.
Lt. Gen. Vincent Stewart, director of the US Defense Intelligence Agency, told lawmakers in May
that the biggest hurdle left in North Korea's missile program is perfecting re-entry.
"It's really a matter of enough trial and error to make that work," Stewart said. "They understand the physics, so it's just a matter of design."
At the current rate of progress, North Korea would ultimately succeed in fielding a nuclear-armed missile capable of threatening the United States, Stewart said.
US commanders are already operating under the assumption
that Kim has the ability to miniaturize a nuclear warhead to place it on a missile.
North Koreans likely judge the progress of their re-entry vehicle using sensors to gauge if the temperature's within a suitable range, said Tong Zhao, a Beijing-based fellow at the Carnegie-Tsinghua Center for Global Policy
's Nuclear Policy Program.
But last week's test involved a whole host of scenarios that could have altered its performance, including launching the missile at lofted trajectory to ensure it didn't travel too far.
Other countries have gone back and retrieved their re-entry vehicles after launch to examine them, but North Korea doesn't have the logistical capability to do so, Zhao said.
"I think the South Koreans were saying, look, this is not the most reliable way to prove the technology. You can only guess to some extent, you can never know for sure if everything will work."
Zhao said he believes the only way to know Pyongyang's operational capability is if the country actually fielded a nuclear warhead atop a missile.
He and other North Korean watchers are concerned that if the world keeps insisting North Korea does not have an ICBM and has not perfected its re-entry technology, Pyongyang could launch a missile with a nuclear warhead just to prove the efficacy of its weapons.
"This will encourage the North Koreans to really want to demonstrate to the international community that they can; therefore, they might actually one day detonate a warhead on top of a missile test," he said. "There is a risk if we keep saying the North Koreans can't achieve the capability."
US envoy's trip to Singapore and Myanmar
The announcement from South Korean authorities comes as US ambassador Joseph Yun, the special representative for North Korea policy, is on his first day
of a weeklong visit to Singapore and Myanmar.
Both of those countries have been previously tied to North Korea's illicit finance activities, which help fund Pyongyang's weapons programs, among other things.
Myanmar has in the past been accused
of purchasing weapons from North Korea, and shipping companies with ties to North Korea have been found operating in Singapore, according to the United Nations.