A training exercise involving U.S. B-52 bombers flying alongside South Korean warplanes was canceled following threats that Pyongyang would withdraw from a highly anticipated summit with President Donald Trump next month, The Wall Street Journal reported, citing U.S. officials.

According to Friday's report, the officials said South Korea had asked to not participate in an air drill that also involved Japan and the U.S.

The White House referred CNBC's request for comment about the Journal report to the Pentagon, which said plans for a separate exercise is continuing as planned.

The news came a day after the Defense Department said the U.S. had no plans to scale back the exercises.

When asked if the U.S. Air Force B-52 Stratofortress, a long-range bomber capable of deploying nuclear weapons, was leaving the exercises, chief Pentagon spokeswoman Dana White said Thursday that the scope of the exercises has not changed.

"These are alliance decisions, this is something that we do to ensure the readiness of both our forces as well as the South Korean forces," White said, noting that the training is "longstanding and defensive in nature."

White also said the Defense Department has not held any talks to scale back its future training operations on the Korean Peninsula.

"There has been no talk of reducing anything, there has been no talk of changing our scope. These are annual exercises and we are very transparent about them," White said.

Meanwhile, White House press secretary Sarah Huckabee Sanders said Thursday that the administration was continuing to prepare for the June 12 summit in Singapore. Soon thereafter, Trump told reporters that if the meeting doesn't happen, the administration will move on.