North Korea launched several projectiles believed to be short-range surface-to-ship cruise missiles from its east coast Thursday, according to South Korea's military.

"North Korea fired multiple unidentified projectiles, assumed to be surface-to-ship missiles, this morning from the vicinity of Wonsan, Gangwon Province," the South Korean Joint Chiefs of Staff (JCS) said, according to the Yonhap News Agency.

The JCS said the South Korean military has beefed up surveillance and vigilance against the possibility of additional provocations, maintaining full preparedness. The statement said the launches were immediately reported to South Korean President Moon Jae-in but gave no further details.

The missiles fired Thursday traveled around 120 miles, according to the South Korean military. The latest provocation came less than a week after United Nations Security Council passed a new resolution expanding sanctions against the country as punishment for its missile tests.

North Korea conducted ballistic missile tests over three consecutive weekends in May going back to Mother's Day, but last weekend there were no launches.

The remote country is on pace to break its record setting 2016 missile test-launch record.

The latest missile tests come as South Korea suspended its use of the American-based missile defense system THAAD.

SOUTH KOREA PUTS THAAD DEPLOYMENT ON HOLD

The Terminal High-Altitude Defense System (THAAD) has already been in operation in southeastern South Korea, with two launchers and radar. The system typically has six launchers – four of which are in in South Korea, but have yet to be installed.

South Korea’s new President, Moon Jae-in, said his office was not briefed on the arrival of four new launchers and ordered an investigation. He also demanded an environmental assessment on the deployment site, saying the country’s Defense Ministry might be attempting to avoid an environmental inspection there.

"Each launch by the DPRK further demonstrates the rationale and necessity of the US-ROK alliance agreement to deploy THAAD," State Department spokesperson Heather Nauert said. "The deployment of THAAD battery to the Korean Peninsula will improve US-ROK joint missile defense posture and enhance our defensive capabilities"

Rep. Adam Smith, the top Democrat on the House Armed Services Committee, called South Korea's decision "a blow to our national security interests."

Smith added that South Korea is "not sure of the U.S. commitment because of Trump's 'America First.'"

"We need to stand as a counter balance for other countries and this is a bad sign," Smith said.

"I have not seen North Korea back down," he added. "If they get nuclear capable missiles, they will threaten and hold sway without being deterred."

On May 14, North Korea premiered a powerful new midrange missile that it said could carry a heavy nuclear warhead. Experts at the time said that rocket flew higher and for a longer time than any other missile previously tested by North Korea, and that it could one day reach targets as far away as Hawaii and Alaska.

There are about 28,500 U.S. troops in South Korea as deterrence against potential aggression from North Korea.

Fox News' Lucas Tomlinson, Jennifer Griffin, Chad Pergram, and the Associated Press contributed to this report.