The Republic of Korea's (ROK) military has said the Democratic People's Republic of Korea (DPRK) resumed flying trash-carrying balloons over the border on Saturday night.

Some 330 trash balloons were detected as of Sunday morning, Yonhap News Agency reported.

The ROK's military said on Sunday it takes the balloons "very seriously" and is on alert to take action in response when necessary. It did not elaborate on what action it would take.

Since last month, the DPRK has floated hundreds of huge balloons, allegedly dumping manure, cigarette butts, scraps of cloth, waste batteries and even dirty diapers on areas across the ROK. 

The DPRK has said its operation was in retaliation for a propaganda campaign by ROK activists, who regularly launch helium-filled balloons to drop anti-Pyongyang leaflets and USB sticks loaded with K-pop music videos and dramas.

On June 2, Pyongyang announced it would temporarily halt sending balloons over the border but warned that it would resume the operation if the ROK sent anti-DPRK leaflets the other way.

In response, the ROK suspended a military agreement with the DPRK on June 4 in order to resume front-line military activities. 

(With input from agencies)