SEOUL, South Korea (AP) — South Korea's military said North Korea fired unidentified projectiles twice Friday into the sea off its eastern coast in its third weapons tests in just over a week.

The North's increased testing activity is seen as brinkmanship aimed at increasing pressure on Seoul and Washington over the slow pace of nuclear negotiations.

Seoul's Joint Chiefs of Staff said the launches were conducted at 2:59 a.m. and 3:23 a.m. from an eastern coastal area but did not immediately confirm how many projectiles were fired or how far they flew.

The North fired short-range ballistic missiles on July 25 and conducted what it described as a test firing of a new multiple rocket launcher system on Wednesday.

Experts say the North is demonstrating its frustration over planned U.S.-South Korea military exercises and stalled nuclear negotiations with the United States, and its weapons tests could intensify if negotiations do not proceed rapidly over the next few months.

By firing weapons that directly threaten South Korea but not the U.S. mainland or its Pacific territories, North Korea also appears to be dialing up pressure on Seoul and testing how far Washington will tolerate its bellicosity without actually causing the nuclear negotiations to collapse, analysts say.

North Korea's state media has said leader Kim Jong Un on Wednesday supervised the first test firing of a new multiple rocket launcher system he said would soon serve a "main role" in his military's land combat operations and create an "inescapable distress to the forces becoming a fat target of the weapon."

The report by North Korea's official Korean Central News Agency differed from the assessment by South Korea's military, which had concluded Wednesday's launches were of two short-range ballistic missiles.

On July 25, North Korea fired two short-range ballistic missiles that Seoul officials said flew 600 kilometers (370 miles) and as high as 50 kilometers (30 miles) before landing in the sea.

North Korea said those tests were designed to deliver a "solemn warning" to South Korea over its purchase of high-tech, U.S.-made fighter jets and the planned military drills, which Pyongyang calls an invasion rehearsal. The North also tested short-range missiles on May 4 and 9.