North Korea fired multiple missiles on Wednesday toward the sea off its east coast, South Korea’s Defense Ministry said, marking Pyongyang’s fourth such weapons launch in a month.

Axar.az reports, citing Reuters, the South Korean military detected the missiles that were fired from the Sondok area, an eastern coastal region of North Korea, the ministry said.

Seoul and Washington were closely analyzing the launch and remained ready to respond to any potential provocation, it said.

North Korea has carried out a series of weapons tests this year, including the launch of a missile that flew more than 550 miles as well as testing hypersonic missiles.

Seoul’s announcement came hours after Kim Yo Jong, the sister of North Korean leader Kim Jong Un, ruled out dialogue with Washington until the U.S. abandoned what she called its hostile policy.

She also repeated Pyongyang’s denial that it was behind the hacking at crypto exchange Binance after the FBI accused North Korea of carrying out the heist.