North Korea’s air force has sharply increased training flights of its fighter jets since July, with the number of sorties reaching as many as 100 a day, a government source said Thursday.

The move is uncommon because North Korean pilots usually focus on ground training in summer.

The communist nation is also showing signs of large-scale artillery exercises along its west coast, and activity of small submarines has also increased, the source said.

These moves could be part of the North’s attempt to raise tensions ahead of South Korea’s presidential election in December.

On Wednesday, South Korean President Lee Myung-bak and top security ministers reaffirmed their pledge to prepare for the possibility of Pyongyang staging premeditated provocations for political purposes and punish such behavior. (Yonhap News)