SEOUL, South Korea (AP) — South Korea’s spy agency told lawmakers Tuesday that North Korea has restarted a plutonium reactor at its main nuclear facility, according to two parliamentary members who attended the closed-door briefing session.

North Korea said in April it would restart the reactor after tensions ran high following its third nuclear test in February, but it has not confirmed that it has done so. Recent satellite photos have shown signs that the reactor may be operating.

The National Intelligence Service told a parliamentary committee meeting Tuesday that North Korea restarted the five-megawatt reactor at its Nyongbyon complex in August but did not say how obtained the information, according to the office of lawmaker Jung Chung-rae.

The office of another lawmaker Cho Won Jin confirmed the spy service presented a similar assessment.

Jung’s office cited the spy agency as saying North Korea also conducted long-range missile engine tests at a northwestern site in August and has moved artillery systems closer to the tense border dividing the peninsula in possible signs of provocation.

Defense officials said the reported engine tests showed North Korea is continuing to pursue its missile programs but do not mean a launch is imminent. They said they have not detected any signs that North Korea’s military has done anything suspicious.

The spy agency declined to comment.

The North Korean nuclear reactor was shuttered under a now-stalled international disarmament-for-aid deal. The reactor can be weaponized to make atomic bombs. Once it is operating, it can produce about 6 kilograms (about 13 pounds) of plutonium a year, enough for one or two bombs. Analysts estimate North Korea already has enough plutonium for between four to eight crude weapons.

North Korea threatened nuclear wars and issued a string of warlike threats this spring, but has gradually ratcheted down the threats and sought to resume cooperation projects with South Korea and stalled six-nation disarmament talks.

Earlier Tuesday, North Korea’s military said its troops had been given an "emergency order" to re-examine operational plans and be ready to launch them to cope with planned trilateral maritime drills by South Korea, the U.S. and Japan this week. South Korea and U.S. officials said the drills in international seas off a southern South Korean island are routine training aimed only at improving readiness to respond to maritime disasters.

Chin Hee-gwan, a North Korea expert at South Korea’s Inje University, said the North’s latest threat shows its frustration at the lack of progress over its push to resume the lucrative cooperation projects with South Korea and the six-party talks. He said Tuesday’s threat wasn’t as serious as those it issued earlier this year and Pyongyang isn’t expected to raise tension again anytime soon as it has to focus on reviving its economy.

The Korean Peninsula officially remains at state of war because the 1950-53 Korean War ended with an armistice, not a peace treaty. About 28,500 American troops are stationed in South Korea.