South Korea has tentatively concluded that two unidentified drones recently found near the border with North Korea are from the communist nation, officials said Wednesday, a finding that raises questions about Seoul's air defense amid heightened military tensions in the region.

South Korea collected two unmanned aerial vehicles near the border -- one found in Paju, just south of the demilitarized zone, on March 24, and the other discovered on Baengnyeong Island near the tensely guarded western maritime border on Monday when North Korea held a live-fire drill.

A team of military officials and experts dissembled the drones to conduct an in-depth analysis and came to the conclusion that Pyongyang has developed the two unmanned aerial vehicles, military and intelligence officials said. The military has not yet officially announced the investigation result.

"According to the analysis of the drones, the two are closely related to one another," a senior military official said, asking for anonymity. "North Korea is believed to have developed the prototype drones for testing to enhance its aerial reconnaissance capability."

Another military source said the aircraft that crashed on Baengnyeong Island was briefly spotted by a radar on Monday, when the two Koreas exchanged hundreds of rounds of fires into the western sea during the North's live-fire drill.