North Korean leader Kim Jong Un. (KCNA via KNS/AFP/Getty Images)

North Korea is pressing ahead with its nuclear weapons program, confirming Tuesday that it has restarted its Yongbyon reactor, the source of its fissile material.

Amid expectations that Pyongyang will mark a key political anniversary next month with a flourish, Kim Jong Un’s regime announced Monday that it was preparing to launch a long-range rocket and declared Tuesday that the Yongbyon facility was operating normally.

North Korean scientists have been “steadily improving the ­levels of nuclear weapons with various missions in quality and quantity,” the official Korean ­Central News Agency quoted the unnamed director of North ­Korea’s Atomic Energy Institute as saying.

The director was speaking to confirm international speculation that its nuclear facility was again operational, the report said. North Korea, in fact, has claimed since 2013 that the reactor was back in service, but that had never been certain to observers outside the country.

“We can definitely say that they are moving ahead and are continuing to grow their nuclear stockpile,” said Melissa Hanham, a researcher at the James Martin Center for Nonproliferation Studies in Monterey, Calif.

Recent commercial satellite imagery indicates North Korea has completed upgrades to launchpads at the Sohae Satellite Launching Station, potentially allowing the country to launch rockets considerably larger than the Unha-3.

Hanham and other experts have been monitoring satellite photos and thermal infrared images from the Yongbyon facility for signs of activity. The pictures suggest that the site is warmer than the area around it, a possible sign of operation.

“This, paired with the announcement of a long-range rocket launch, suggests that they’re making plans for the 70th anniversary,” she said.

North Korea is preparing to celebrate the foundation of its communist Workers’ Party on Oct. 10 with great fanfare — soldiers and students have been practicing for the parade for months — and perhaps a show of military force.

Without giving a time frame, North Korea said Monday that it was preparing to launch a long-range rocket, reportedly for its space research program.

“The world will clearly see a series of satellites of [North] Korea soaring into the sky at the times and locations determined by the Central Committee of the Workers’ Party of Korea,” KCNA quoted the director of the country’s National Aerospace Development Administration as saying.

What life looks like inside North Korea: Scenes from inside the hermit kingdom. (Dita Alangkara/AP)

South Korea’s Defense Ministry said last week that satellite imagery showed North Korea had completed a 220-foot-tall tower at its Sohae rocket-launch facility in Dongchang-ri, on the west coast.

North Korea has previously launched “rockets” as part of its ostensible space program, and it denies violating any international missile bans by doing so. But any launch would be seen by the outside world as a part of its efforts to test an intercontinental ballistic missile capable of hitting the U.S. mainland and a clear contravention of U.N. Security Council resolutions.

Tuesday’s statement appeared to confirm what analysts had been seeing for some time and what North Korea itself has previously announced: It restarted the Yongbyon facility in April 2013, shortly after its third nuclear test.

Yongbyon has been the focus of multilateral negotiations to persuade North Korea to give up its nuclear ambitions. The facility ­includes a 5-megawatt plutonium reactor and a uranium-enrichment plant, and it is thought to be the source of the weapons-grade material used in the country’s three nuclear tests.

The reactor was shut down in 2007 in a deal brokered through “six party” talks involving the United States, China, Russia, ­Japan and the two Koreas.

However, after it conducted its third nuclear test, in February 2013, North Korea threatened to restart the reactor.

“If the U.S. and other hostile forces persistently seek their reckless, hostile policy towards the DPRK and behave mischievously, the DPRK is fully ready to cope with them with nuclear weapons any time,” KCNA said Tuesday, using the official abbreviation for North Korea.

While analysts said that Tuesday’s threats appeared to be routine, they warned that there was firepower behind them.

“Behind the standard rhetoric, there is a substantive message,” said Joel Wit, a former American diplomat now at the U.S.-Korea Institute of the School of Advanced International Studies at Johns Hopkins University. “It’s hard to tell exactly what’s going on, but it looks like North Korea is about to start, or has already started, to produce more material for nuclear weapons.”

Under Kim Jong Un, North Korea has insisted that it be accepted as a nuclear weapons state and said it has no interest in an Iran-style deal to scale back its nuclear ­program.

The State Department said Tuesday that it would not accept North Korea as a nuclear state. “We call on North Korea to refrain from irresponsible provocations that aggravate regional tensions, and to instead focus on fulfilling its international obligations and commitments,” said Katina Adams, a spokeswoman for the department.

Hanham, in Monterey, said the latest claims show that none of the inducements previously offered to North Korea — such as heavy fuel oil as an alternative to nuclear energy — have worked.

That means that for now, deterrence and containment remain the best options, said Daniel Pinkston, a nonproliferation expert currently at Babes-Bolyai University in Romania. “There was no war yesterday, and there’s no war today,” Pinkston said.

Carol Morello in Washington contributed to this report.