SEOUL — South Korea said Friday it has resumed blasting propaganda broadcasts into North Korea to retaliate against the North's latest round of trash-carrying balloon launches, a resumption of Cold War-style tactics that are raising animosities between the rivals.

South Korea's Joint Chiefs of Staff said in a statement that it used frontline loudspeakers to blare anti-Pyongyang broadcasts over the border between Thursday evening and Friday morning.

The broadcasts were the first of their kind in about 40 days. The contents of the broadcasts were not immediately known, but their previous ones on June 9 reportedly included K-pop songs, weather forecasts and news on Samsung, the biggest South Korean company, as well as outside criticism of the North's missile program and its crackdown on foreign video.

The South Korean broadcasts could trigger an angry response from North Korea, which is extremely sensitive to any outside attempt to undermine its political system.

In 2015, when South Korea restarted loudspeaker broadcasts for the first time in 11 years, North Korea fired artillery rounds across the border, prompting the South to return fire, according to South Korean officials.

No casualties were reported.

South Korea's military earlier said North Korea floated the balloons on Thursday afternoon in its seventh such balloon campaign in recent months.

Earlier this week, the powerful sister of North Korean leader Kim Jong Un hinted at flying rubbish-carrying balloons again or launching new countermeasures, saying South Korean balloons have been found again at the border and other areas in North Korea.

In her statement Tuesday, Kim Yo Jong warned that South Korean "scum" must be ready to pay "a gruesome and dear price." That raised concerns that North Korea could stage physical provocations, rather than balloon launches.

South Korea's military said Wednesday it has boosted its readiness to brace for any provocation by North Korea. It said North Korea may fire at incoming South Korean balloons across the border or floating mines downriver.

It was not immediately known whether groups in South Korea had recently scattered leaflets in North Korea.

For years, activist groups led by North Korean defectors have used helium-filled balloons to drop anti-North Korean leaflets, USB sticks containing K-pop music and South Korean dramas and US dollar bills in the North.

Tensions between the Koreas have heightened in recent years because of North Korea's missile tests and the expansion of US-South Korean military drills that North Korea calls invasion rehearsals.

Experts said North Korea's expanding ties with Russia could embolden Kim Jong Un to stage bigger provocations, particularly ahead of the US presidential election in November.

North Korea's state media said Friday that Kim met a visiting Russian delegation led by Vice Defense Minister Aleksey Krivoruchko.

During the meeting, Kim stressed the need for the two countries' armies to unite more firmly to defend international peace and justice, according to the North's official Korean Central News Agency.