SEOUL, South Korea — The U.S. is threatening a nuclear attack against North Korea by flying B-52 bombers during joint military drills with South Korea this month, the North’s National Defense Commission said Thursday.

The B-52 bombers taking part in the Aug. 19-30 Ulchi Freedom Guardian exercises are a “brazen” nuclear threat, the Commission, led by dictator Kim Jong Un, said in a statement. U.S. Forces Korea declined to say if B-52s have joined the drills.

“Our revolutionary forces are sharply observing every move of the nuclear bombing squad through our cross hairs,” the NDC said via the official Korean Central News Agency.

In March, Kim raised tension by ordering his generals to prepare nuclear attacks on the United States after two B-2 bombers flew over the Korean Peninsula during annual U.S.-South Korean drills. B-52 bombers also joined the drills that month, according to the Pentagon.

In a statement issued Thursday, U.S. Forces Korea spokesman Christopher Bush said the drill “is defense-oriented and is an annual event.” He didn’t answer a question about whether B-52 bombers took part.

The renewal of militant rhetoric from the North’s top ruling body contrasts with signs of a thaw in relations after North and South Korea agreed Aug. 14 on reopening a jointly run factory park shuttered in April amid heightening tension.

KAESONG RESTART

The two sides moved closer to restarting Kaeseong Thursday with an agreement to form a joint committee to oversee the process.

A U.S. envoy plans to travel to Pyongyang Friday at the invitation of the North in an effort to bring back an American detained there since November, the State Department said. A Chinese nuclear envoy visited the North and met with a senior North Korean official earlier this week, according to KCNA.

In February, the North conducted its third nuclear test in what it called a deterrent act against U.S. hostility, prompting the United Nations to tighten its sanctions against the country.

North Korea “has recklessly tested missiles and nuclear devices,” Defense Secretary Chuck Hagel said at a security forum in Brunei, according to prepared remarks. “They need to rejoin the international community by meeting their obligations under U.N. resolutions. Until then, the United States will continue to work with our allies to deter North Korean aggression.”

About 28,500 U.S. troops are stationed in South Korea as a deterrent against North Korea, a legacy of the 1950-53 Korean War that ended in a truce.