Military exercises between South Korea and the United States have little effect on Pyongyang's relations with either Washington or Seoul despite bellicose war threats the communist nation makes against such exercises, a U.S. expert said Monday.

North Korea harshly denounces annual military exercises South Korea holds with the U.S. as a preparation for war against it.

Ahead of the latest round of drills, the Ulchi Freedom Guardian, which kicked off Monday, Pyongyang also threatened to take its strongest military counteraction unless the exercises were canceled.

Despite such rhetoric, the exercises do not have lasting effects and the situation usually gets back to where it was before the exercises, said Victor Cha, chief Korea analyst at the Center for Strategic and International Studies, in a report after analyzing 10 years of U.S.-South Korea military exercises from 2005-2014.

"U.S.-ROK military exercises have a null effect in the overall U.S.-DPRK diplomatic relationship. They are not game-changers.  The past 10 years of exercises demonstrated a rough correlation with the status of bilateral relationship prior to the exercises," Cha said.

"If U.S.-DPRK relations were coded positively prior to the exercises, it remained positive after the exercise, despite North Korean rhetoric on the contrary. On the other hand, if the relationship was coded negatively prior to the exercises, the exercises tended to reinforce the negative relations in terms of both rhetoric and possible provocations," he said.

The North can also "insulate" positive inter-Korean relations from its belligerence against the U.S. during the exercise period, Cha said, adding that inter-Korean ties in 2005 and 2006 remained good despite belligerence against the military exercises. 

Cha, however, noted that small-scale North Korean provocations during and after the exercise period became more common after 2009.

"Pyongyang's official rhetoric remains a good indicator of possible small-scale provocative actions during the exercise period. Washington and Seoul would do well to listen carefully to Pyongyang's rhetoric in the coming days for potential actions," he said.

South Korea and the U.S. have long argued that their annual drills are purely defensive in nature.

On Monday, State Department spokesman John Kirby reiterated this point.

"These exercises have been long planned and they are exercises that we routinely do with our allies in South Korea and you're right, they have started. They're proceeding normally and apace and we look forward to completing the exercise with them as we always do," Kirby said.

"This is about improving alliance capabilities and meeting our security commitments there in the region and on the Korean Peninsula and nothing more than that," he said.

The latest exercise UFC is the world's largest computerized military drill aimed at defending the South from a North Korean attack, involving nearly 80,000 South Korean and U.S. troops.

This year's exercise came amid unusually heightened military tension between the two Koreas following the North's detonation of land mines on the South Korean side of the demilitarized zone earlier this month. (Yonhap)