North Korea has carried five nuclear tests in the past decade.
South Korea is examining the possibility of leasing a reconnaissance satellite to monitor the activities of the North Korean military, Yonhap news agency quoted officials of the Ministry of National Defense (MND) as saying on 18 October.
The missile launched in June flew 400 kilometers into the Sea of Japan and this was celebrated by the North Korean leader, Kim Jong Un. "We will not step back as long as there's a nuclear threat to us from the United States".
Lee stated, "A preemptive nuclear strike is not something the US has a monopoly on". But such a move likely requires discussions with the USA, which plays a vital role in South Korea's defense.
"If they continue at this rate, the Musudan intermediate-range ballistic missile could enter operational service sometime next year - much sooner than had previously been expected", said John Schilling, an aerospace engineer with expertise in Pyongyang's missile programmes.
During their visit to the USA, foreign minister Yun Byung-se and defense minister Han Min-koo will seek response measures against North Korea's nuclear threats.
The U.N. Security Council is strongly condemning North Korea's latest ballistic missile launch, which failed, as a "grave violation" of its sanctions banning such tests.
North Korea claims it has the technology to develop a miniaturized nuclear warhead and place it atop such a missile. Lee said that the country may undertake "a sixth, a seventh, or an eighth" nuclear test in the future.
U.S. Defense Secretary Ash Carter said at the start of talks in Washington between the foreign and defense ministers of the United States and South Korea that the U.S. commitment to provide "extended deterrence, guaranteed by the full spectrum of U.S. defense capabilities" was "unwavering".
But going nuclear isn't the only lofty ambition for the hermit kingdom.
Kerry called for every country to rigorously enforce United Nations sanctions on North Korea, which are intended - but have failed - to prevent its development of weapons of mass destruction.
"We will discuss ways to ensure that the extended deterrence - including the nuclear umbrella of the USA - will be implemented, along with various ways to strengthen the Seoul-Washington alliance".
North Korea's intermediate-range ballistic missile (IRBM) could be ready to go much earlier than initially expected, says a US -based think tank.
The projectile, believed to be a Musudan missile, was sacked from near an airfield in the western city of Kusong, at 12:33 a.m. And the UN Security Council also strongly condemned Pyongyang's missile launch in a closed door meeting in NY on Monday, local time.