SEOUL, South Korea--North Korea will keep improving its nuclear and long-range ballistic missile capabilities next year to gain leverage to force Washington to make concessions, like the easing of sanctions, government and private analysts in South Korea said Tuesday.

The isolated North has made major strides this year in its nuclear weapons program but has also faced increasingly tough U.N. sanctions. On Sept. 3, it detonated what it called a hydrogen bomb in its sixth and most powerful nuclear test. It has also launched three intercontinental ballistic missiles this year, demonstrating rockets powerful enough to deliver warheads to all of the continental United States.

After its last ICBM test, conducted Nov. 29, North Korea claimed to have completed building its nuclear force. But the country has yet to clear a key technological hurdle: proving that its warheads can survive re-entry into the atmosphere after flying through space, according to Western officials and analysts.

Forecasting North Korea’s nuclear weapons program for the new year, the Unification Ministry in South Korea said Tuesday that the North “will continue to advance its nuclear and missile capabilities” in 2018 despite its claims about completing its nuclear force.

North Korea will conduct at least one more missile test to master the re-entry technology for its warheads, analysts said. But the North also was racing against time to secure full ICBM capabilities before new U.N. sanctions begin squeezing its economy, they said.

“Re-entry is a question North Korea must solve to boost its negotiating leverage and for its military and technological purposes,” Shin Beom-chul, a security analyst, said in a report published over the weekend by the government-run Institute of Foreign Affairs and National Security in Seoul. “For North Korea, there is a big difference between entering negotiations with the United States after acquiring full ICBM capabilities and starting such talks without them.”

North Korea wants Washington to recognize it as a nuclear weapons state.

With that status, analysts said, the North would seek arms-reduction talks in hopes of gaining concessions from Washington, such as easing sanctions and reducing the U.S. military presence around the Korean Peninsula. In return, Pyongyang could offer to freeze or give up its ICBMs while retaining the rest of its nuclear capabilities, analysts said.

So far, all of the North’s three ICBM tests have taken place in the sea between North Korea and Japan. Although the missiles soared to extremely high altitudes, demonstrating their power, they never flew beyond Japan.

Analysts warned that in its next long-range missile test, the North could launch a missile on a full ICBM trajectory and even carry a live nuclear warhead to demonstrate its mastery of warhead re-entry technology.

“The North’s seventh nuclear test could take place not underground but over the Pacific,” Cheong Seong-chang, a senior analyst, said in a report published by the independent Sejong Institute of South Korea.

In September, North Korea’s leader, Kim Jong Un, vowed to take the “highest level of hard-line countermeasure in history” after President Donald Trump threatened to “totally destroy North Korea” if it continued to threaten the United States and its allies. The North’s foreign minister, Ri Yong Ho, later said that Kim might be considering an atmospheric hydrogen bomb test over the Pacific Ocean.

The U.N. Security Council has slapped North Korea with four rounds of sanctions this year alone, seeking to deprive the country of key sources of hard currency by banning its exports of coal, iron ore and sea products and phasing out the use of North Korean workers abroad. It also tried to squeeze the North’s fuel supplies by demanding that member nations drastically reduce exports of refined oil to North Korea.

From January to November, North Korea’s trade with China, its only major remaining trading partner, declined to $4.7 billion, a drop of more than 10 percent, the Unification Ministry said Tuesday. Its exports to China plummeted nearly 32 percent in the same period, the ministry said.

On Tuesday, the Treasury Department imposed sanctions on two senior North Korean officials for their work on the country’s ballistic missile program.

One of the officials, Kim Jong Sik, was reportedly crucial to North Korea’s efforts to develop solid fuel rockets, which are more difficult to defend against because they can be launched quickly. Liquid fuel rockets can take hours to fuel. The other official, Ri Pyong Chol, is said to have played a key role in developing North Korea’s intercontinental ballistic missile program, the Treasury Department reported.

The sanctions mean that the Treasury Department could, among other things, seize any assets held by the men in the United States. Although it is unlikely that either official owns property or has bank accounts in the United States or other Western countries, the sanctions are intended to increase pressure on North Korea to halt its nuclear and ballistic missile weapons programs, a campaign that has so far shown no signs of working.

U.S. officials say they still favor a diplomatic solution to the North Korean crisis. But top aides to Trump, including Gen. H.R. McMaster, his national security adviser, have indicated that Washington was also considering a military action against the North.

Increasingly anxious over possible military conflict, President Moon Jae-in of South Korea proposed this month that his country and the United States postpone their joint military exercises, which were originally expected to start in late February.

Moon said the annual exercises, which North Korea has denounced as rehearsals for an invasion, could be postponed until after South Korea hosted the Winter Olympics in February and the Paralympics in March. Whether the allies will eventually delay the drills depends on whether North Korea conducts any weapons tests in the weeks leading up to the games, South Korean officials said.

Moon hopes to create a lull in the nuclear standoff during the Olympics and use it as momentum to start talks with North Korea. When North Korea said it completed its nuclear force following its ICBM test in November, some analysts said the North might now be open to stopping its program there and to start negotiating.

Reacting to the latest U.N. sanctions resolution, the North Korean Foreign Ministry said Sunday that the country “will further consolidate our self-defensive nuclear deterrence.” But it did not specify any missile or nuclear tests.

Instead, North Korea might be preparing for a satellite launch, the South Korean newspaper JoongAng Ilbo said Tuesday, citing an anonymous government source.

South Korea saw “nothing out of ordinary at this moment” while it and the United States were closely monitoring for possible provocations from the North, Noh Jae-chon, a South Korean military spokesman, said Tuesday.

North Korea launched a rocket to put a satellite into orbit in 2012 and again in February last year. The United Nations bans North Korea from launching satellites, fearing that the country was using the program as a cover for developing long-range ballistic missiles.

(Dec. 26, 2017)