North Korea on Sunday morning fired several cruise missiles into the sea between the Korean Peninsula and Japan, according to South Korea’s Joint Chiefs of Staff.

The JCS said in a message to reporters that the missiles landed at around 8 a.m. in waters near the North Korean port city of Sinpo, South Hamgyong Province, on the eastern coast. “Our military is closely coordinating with the US side amid heightened vigilance and surveillance, and watching for further signs and activities from North Korea,” it said.

No other details were provided by the JCS as of Sunday afternoon.

Experts in Seoul pointed out that Sinpo is where North Korea’s submarines are designed and built. Yang Uk, a senior researcher at the Asan Institute of Policy Studies, told The Korea Herald that given the location, there was a possibility of submarine-launched cruise missiles.

Last week, North Korea fired cruise missiles toward the sea off the west coast, which it claimed to be Pulhwasal-3-31 updated cruise missiles, speculated as capable of carrying nuclear warheads.

North Korea has been continuing a streak of military provocations since the turn of the new year. Its leader, Kim Jong-un, warned in his latest round of rhetoric that he would write into the country’s constitution a “full occupation” of South Korea in the event of a war.

For three days from Jan. 5, North Korea fired hundreds of artillery shells near the shared border. Then it carried out a test of an intermediate-range ballistic missile on Jan. 14 and an underwater nuclear weapons systems on Jan. 19.

The South Korean military and intelligence authorities are wary of North Korea intensifying its belligerence to coincide with the parliamentary election in Seoul in April and the presidential election in Washington in November.

South Korea's Minister of National Defense Shin Won-sik said in an interview with The Korea Herald on Jan. 22 that Kim would try to step up military tensions in a bid to get the next US president to accede to his demands.

The minister said the North Korean leader may undertake a nuclear weapons test if he feels doing so could “get the incoming administration in Washington to pivot to a policy of engagement of appeasement, and away from containment.”