SEOUL — South Korean troops mounted massive search operations and roadblocks Tuesday after signs of a possible breach of the Demilitarized Zone were discovered early in the morning.

But late Tuesday, a senior South Korean military official said the cuts could have been made by a South Korean civilian trying to defect to North Korea, instead of North Korean agents infiltrating the South.

According to the South Korean Joint Chiefs of Staff, three 15-inch by 15-inch holes were found in the two-layer wire fence that marks the DMZ’s southern boundary near Cheolwon, northeast of Seoul.

A South Korean border patrol found the holes around 2 a.m., Brig. Gen. Hwang Jung-seon of the Joint Chiefs told reporters around noon Tuesday.

“Both search operations and an investigation are under way, taking several possibilities into consideration,” Hwang said, without elaborating on what the possibilities were. “An operation is under way to deal with any possible infiltration by the enemy.”

But by late Tuesday afternoon, Hwang said it was possible the cuts were not made by North Koreans.

“That was not an expert infiltration method by the enemy. It lacks the restoration of the area to normal,” Hwang told reporters. “I believe that it was an act done by a person who knows the area well.”

Hwang said a preliminary investigation found that footprints found in the area headed north instead of south. Though the military believes the cuts were most likely not made by North Koreans, the investigation will continue, Hwang said.

If it was someone headed north, it would likely be a civilian, because military units in the area did not report any missing soldiers Tuesday, Hwang said.

Officials at U.S. Forces Korea declined to comment on the situation, referring questions to the South Korean Defense Ministry.

U.S. Secretary of State Colin Powell said early Tuesday afternoon he had information confirming the breach but had not spoken with South Korean officials about the matter.

“It did not come up in our discussions,” Powell said after meeting with Foreign Minister Ban Ki-moon Tuesday at the Ministry of Foreign Affairs and Trade in Seoul. “I got word earlier this morning that there was an apparent small breach in the wire system at the DMZ. It’s being looked into. That’s the extent of the information.”

Powell was in Seoul as part of a three-country tour to urge North Korea to resume talks about its nuclear program. The secretary also visited Japan and China in an effort to build support to urge North Korea back to the negotiating table.

After the discovery was made, the South Korean military raised its alert level to “Jindokgae hana,” the highest on its scale. The alert level was lowered slightly by Tuesday night, officials said.

Roadblocks and traffic checkpoints were set up at various points near the DMZ, officials said.

Incursions along the DMZ, once relatively common in the fragile ceasefire that ended the fighting of the Korean War, have been rare in the past five years. In September 1996, 24 North Korean crewmen were killed in South Korea after their submarine ran aground off the coast of South Korea.

Five South Korean soldiers and three civilians were killed in the hunt for the North Koreans.

If Tuesday’s incident turns out to be an infiltration by the North, it would be the first since 2000, South Korean military officials said.

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