TOKYOTOKYO (Reuters) - U.S. Defense Secretary Mark Esper said on Tuesday that the United States will not overreact to a series of missiles launches by North Korea in recent weeks and would keep the door open to talks with Pyongyang.

North Korea fired missiles into the sea off its east coast for the fourth time in less than two weeks, the South Korean military said on Tuesday, as Pyongyang protested that joint U.S.-South Korea military drills violated diplomatic agreements.

"The key is to keep the door open for diplomacy... we're not going to over react to these, but we monitor them, we watch them closely and we're cognizant of what's happening," Esper told reporters traveling with him to Japan.

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He added that the missiles launched on Tuesday were short-range ballistic ones and he would be speaking about North Korea with his counterparts in Japan and South Korean during his upcoming visit to both countries.

U.S. President Donald Trump and North Korean leader Kim Jong Un met on June 30, but Pyongyang has since accused Washington of breaking a promise by planning the military exercises and warned the drills could derail talks.

North Korea said on Tuesday that the joint military drill being conducted by the United States and South Korea violates agreements North Korea made with them.

Esper said the current exercise with South Korea, known as Dong Maeng and largely computer simulated, was underway and at this point there was no plan to alter future joint military drills with Seoul.

On Friday, Trump sought to play down recent short-range missile tests, saying they did not break any agreement he had with Kim.

Talks between the United States and North Korea have stalled, and policy analysts believe the tests are designed both to improve North Korean military capabilities and to pressure the United States to offer more concessions.

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A senior U.S. defense official, speaking on the condition of anonymity, said the United States had not seen the progress from North Korea that they would have liked and Pyongyang had not reciprocated Washington's gesture in suspending and altering a number of exercises over the past year.

SOUTH KOREA-JAPAN DISPUTE

South Korea has said it is exploring all options in a bitter trade row with Japan, including scrapping an intelligence sharing pact.

Tensions between Japan and South Korea escalated on Friday when Japan removed South Korea from a favored trading nations list, prompting Seoul to warn it would not be defeated again by its neighbor, laying bare decades-old war time animosity.

One victim of the tensions could be an accord that facilitates three-way intelligence gathering with Washington, and is crucial for both South Korea and Japan in dealing with North Korea's nuclear and missile threats.

"I would obviously encourage that type of intel sharing to continue, it's key to us," Esper said.

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"I would ask them to both resolve this issue quickly and let's really focus on North Korea and China," he added.