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Ahn Young-joon, Associated Press
North Koran defectors carry plastic bags containing leaflets condemning North Korean leader Kim Jong Un and his government's policies which are attached to balloons in Paju, near the border with North Korea, South Korea, Friday, Oct. 10, 2014. For the first time in three years, North Korean leader Kim Jong Un didn't appear at a celebration of the anniversary of the founding of the ruling Workers' Party on Friday, further increasing speculation that something is amiss with the authoritarian leader who hasn't been seen publicly in more than a month.

SEOUL, South Korea — North and South Korea traded machine-gun and rifle fire Friday after South Korean activists released anti-Pyongyang propaganda balloons across the border, officials said, a reminder of the bitter rivals' animosity despite some recent glimmers of trust building.

North Korea opened fire nearly two hours after the release of the balloons and several machine-gun bullets fell south of the border near a South Korean base and a residential area, Defense Ministry spokesman Kim Min-seok said.

He said South Korea then fired 40 rounds from machine guns. North Korea then opened fire with rifles, which South Korean soldiers responded to in kind, Kim said. There were no reports of damage or injuries. It wasn't immediately clear if North Korea was firing at the balloons.

The Defense Ministry was holding an emergency meeting. Some residents of Yeoncheon, a town near the border, evacuated after the gunfire, according to Im Doo-jin, a village official responsible for civil defense training.

The exchange of fire comes as speculation grows about the condition of North Korea's authoritarian leader, Kim Jong Un, who has been out of public view for more than a month. He missed a major event on Friday, the founding anniversary of the North's ruling Workers' Party, for the first time in three years.

South Korean activists and North Korean defectors frequently release balloons carrying leaflets into the North, but Friday's action was especially provoking because it came on the anniversary.

South Korean civic organizations mainly made up of North Korean defectors sent balloons from several areas along the border, including 10 balloons from Paju that contained 200,000 anti-North Korea leaflets, 1,000 U.S. $1 bills, 400 propaganda DVDs and 300 propaganda USB thumb drives.

North Korea's Secretariat of the Committee for the Peaceful Reunification of Korea released a statement Thursday criticizing the planned leaflet launch, calling it "little short of a declaration of a war."

"If the South Korean authorities allow or connive at the projected leaflet-scattering operation, the north-south relations will again be pushed to an uncontrollable catastrophe and the provokers will be wholly accountable for it," the statement said.

North Korea has issued similar warnings about leaflets in the past but hasn't acted on its threats. South Korea has responded that it can't ban activists from launching leaflets because of the country's freedom of speech.

Hopes for better ties between the countries, which fought a devastating three-year war in the 1950s and are still divided by the world's most heavily armed border, had risen somewhat after a senior-level North Korean delegation made a surprise visit to the South last week and met with South Korean leaders. The two sides agreed to resume talks among senior officials.

But there has also been lots of speculation about the health of North Korean leader Kim Jong Un.

Indications that Kim remains firmly in power were evident, however. His name appeared on a flower basket placed before statues of his father and grandfather, both of whom also ruled North Korea, and an earlier dispatch said the might of the party "is growing stronger under the seasoned guidance of Marshal Kim Jong Un."

State media haven't shown Kim, who is thought to be 31, performing his customary public duties since he attended a concert on Sept. 3. He had been walking with a limp and was more overweight than usual in images broadcast before that. An official documentary from late last month described him as dealing with "discomfort," which led to international speculation that he may be ill.

Much of what happens in Pyongyang's inner circles is hidden from the eyes of outsiders and even from average North Koreans. This leaves media in South Korea and elsewhere to speculate, sometimes wildly, about what's really happening. Some reports indicate that Kim could have gout, diabetes or other ailments, with much of the speculation based on that single reference in the documentary and unidentified sources speaking to South Korean media.

South Korean officials played down the speculation and said Kim appears to be in charge of key affairs.

Associated Press writer Hyung-jin Kim contributed to this story.