A planned flight of B-52 Stratofortress bombers to the Korean Peninsula was re-routed due to South Korean concerns it would escalate tensions ahead of the historic June 12 summit in Singapore between President Donald Trump and North Korean leader Kim Jong Un, the Wall Street Journal reported, citing U.S. officials.

The Journal was referencing the U.S. military’s “Continuous Bomber Presence missions,” according to Marine Lt. Col. Christopher Logan, a Pentagon spokesman. However, Logan wouldn’t comment on whether B-52 flights had their courses adjusted in light of South Korean concerns.

"[These] missions are part of a routine, forward deployed, deterrence capability supporting regional security and our allies in the Indo-Pacific region,” he said. “We continue to coordinate with our allies on these missions, but for operational security reasons we cannot comment on future or ongoing operations. This would also include our decision-making process as it relates to operations."

According to the Wall Street Journal’s sources, South Korean officials said they did not want to participate in the mission involving the bombers due to concerns that the flights would antagonize their North Korean counterparts. The U.S. bombers carried out the second part of their mission, a training exercise with Japanese aircraft, according to the Journal.

At a briefing Thursday, Pentagon spokeswoman Dana White pushed back against reports that B-52s had been cut from a separate joint training exercise on the Korean Peninsula called “Max Thunder.”

“The scope of our exercises has not changed,” she said about Max Thunder. “I won’t be able to speak to specific details, but our exercises are annual. They’ve been longstanding. They’re defensive in nature, and they will continue.”

North Korea’s state-run news service called Max Thunder a "provocation" and alleged that it is a test run for an invasion of North Korea. The mission that would have involved the B-52s was reportedly a separate endeavor, Blue Lightning, that is part of the Continuous Bomber Presence.

Max Thunder, which began last week, is mostly a joint U.S.-South Korean air exercise, involving about 100 aircraft from both countries training together over a two-week period.

North Korea was reportedly concerned about the presence of so many U.S. air assets in the exercise. However, Max Thunder appears to be going ahead as planned, while the B-52s adjusted their flight paths.

CNN reported that a flight of two B-52s were shifted from a planned route that would have taken them over the Korean Peninsula.

Officials told CNN that the B-52s took off from Guam and conducted a 24- to 48-hour flight that flew to the south and southeast, but did not enter South Korean airspace, before returning.

In recent months, U.S. bombers have been regularly spotted flying over the peninsula as the tension between the two Koreas headed toward a boiling point. B-52s are noteworthy for their range and capability of deploying nuclear weapons.