(Yonhap) -- Despite signs of warming inter-Korean ties, South Korea's defense minister on Wednesday pledged firm military readiness to counter any provocations by North Korea that he considers "unpredictable."

Kim Kwan-jin made the remark during a meeting of retired generals at a time when relations between the two Koreas have shown signs of improvement in light of the recent reunions of families separated since the 1950-53 Korean War.

Hundreds of separated families met in a tearful reunion at North Korea's Mount Kumgang resort from Feb. 20-25, although South Korea and the United States on Monday began their annual joint drills despite Pyongyang's repeated warnings.

"The Kim Jong-un regime has continuously developed nuclear and missile programs, and increased conventional weapons," Kim said in a congratulatory address. 

"It is very hard to predict what will come next as Kim Jong-un could hurriedly make a wrong judgment under the unstable political situation...Our military is prepared to counter any provocations."

His remark came after a North Korean patrol ship violated the tensely guarded western maritime border several times and retreated Monday night, on the first day when South Korean and U.S. forces began their joint drills while family reunions were still underway.

Seoul's defense ministry considered the North's border violation as an attempt to test the South Korean forces, saying it is looking into possibilities that the North Korean vessel intentionally crossed the western border.

Seoul and Washington were expected to stage relatively low-profile drills this year so as not to provoke the North, but their drills drew fierce criticism from the communist state, which sees them as a rehearsal for a northward invasion. The allies have claimed the exercises are defensive in nature.