South Korean Marines move into position on a beach during a joint landing operation by US and South Korean Marines in the southeastern port of Pohang, Korea.

The Pentagon defended the ongoing joint U.S. and South Korean military exercises Thursday amid North Korean threats of withdrawing from a highly anticipated summit with President Donald Trump next month.

"The scope of our exercises has not changed," chief Pentagon spokeswoman Dana White said, adding that the annual drills are "longstanding and defensive in nature."

"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 will continue despite the planned talks with North Korea.

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.

At the Pentagon, White 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.

The North's state-run news agency described the bilateral military drill dubbed "Max Thunder," as a "provocation" and a test run for a future invasion.

Lisa Collins, a fellow with the Korea Chair at the Center for Strategic and International Studies, described Pyongyang's reaction to the planned military exercises as a "cover to express their dissatisfaction with a bunch of different issues."

"North Korea does normally take issue with military exercises, but these were announced several weeks ago and even the South Koreans said that Kim Jong Un was willing to overlook the U.S. and South Korean exercises happening in the region," Collins said in a previous interview with CNBC.

Collins also said she expects the reclusive leader from the North to attend the meeting with Trump.