North Korea has again taken to launching what appear to be trash-laden balloons south, according to South Korea's military.

South Korea's Joint Chiefs of Staff on Monday said in a statement that North Korean balloons were moving in a southerly direction.

"Citizens are advised to be cautious of falling debris," the Joint Chiefs of Staff said. "If you find any fallen balloons do not touch them and report them to the nearest military unit or police station." 

City authorities Seoul also issued a warning to residents late on Monday, saying at least one of the balloons "has been confirmed to have entered Seoul's airspace. 

Tensions are always high between the two neighbors, still not formally at peace following the Korean War of the early 1950s.

But Russian President Vladimir Putin's first trip to North Korea in more than 20 years last week, signing a strategic partnership deal that's said to include a mutual defense clause, prompted fresh concern in the South.

No highly hazardous materials in first balloons, but signs of poverty

Starting in late May, hundreds of trash and excrement filled balloons were floated over the border in what Pyongyang said was retalliation for balloons carrying anti-regime propaganda.

North Korea is particularly sensitive to this given the efforts it goes to ban access to foreign news for its roughly 26 million residents. Previously, South Korea tried to stop activists from targeting the North Korean population, but this ban was successfully challenged before court last year.

North Korean state media reported early in June that the launching of North Korean balloons was being suspended, saying that they had been a "thorough countermeasure."

Following the first wave of drops, South Korean officials said no highly dangerous materials were found in the balloons.

It did however provide insights into the continuing degree of shortages in North Korea, at least according to the South's Unification Ministry, which said it found evidence of fertilizer that used human feces. Fertilizer was one product the North used to depend on its southern neighbor for, until deliveries were halted in response to Pyongyang's weapons testing in 2007.

kb, msh/dj (AP, Reuters)