South Korean and US soldiers wrestle for photographers during a joint annual winter exercise in Pyeongchang, on January 28, 2016.

South Korea and the U.S. are eliminating their massive springtime military drills and replacing them with smaller exercises in what they call an effort to support diplomacy aimed at resolving the North Korean nuclear crisis.

The decision announced by both countries Sunday came after President Donald Trump complained about the cost of joint drills even as his high-stakes second summit with North Korean leader Kim Jong Un collapsed last week.

The drills' cancellation is an olive branch to North Korea, which has viewed them as an invasion rehearsal. But some experts say it will likely weaken the allies' military readiness amid worries that tensions erupt again in the wake of the failed nuclear summit in Vietnam.

The Pentagon said in a release that the U.S. and South Korean defense chiefs decided to conclude the Key Resolve and Foal Eagle series of exercises. It said the allies agreed to maintain firm military readiness through newly designed command post exercises and revised field training programs.

Acting U.S. Secretary of Defense Patrick Shanahan and South Korean Defense Minister Jeong Kyeong-doo "made clear that the alliance decision to adapt our training program reflected our desire to reduce tension and support our diplomatic efforts to achieve complete denuclearization of the Korean Peninsula in a final, fully verified manner," the statement said.

Seoul's Defense Ministry released a similar statement.

Jeong expressed his regrets at the lack of agreement at the Trump-Kim summit but still hopes that Washington and Pyongyang will continue negotiations, the South Korean statement said.

The new training, dubbed "Dong Maeng," which means "alliance" in English, starts Monday and runs through March 12. It will focus on "strategic operational and tactical aspects of general military operations on the Korean Peninsula," South Korea's military and the U.S.-South Korean combined forces command said in a joint statement.