North Korea's military has sharply increased drone sorties along the western part of its border with South Korea, a government official said Tuesday.

"Drone activity has increased sharply around the western part of the frontline as of late," the official said, asking not to be identified. 

"There is a brisk pace of take-off and landing exercises involving various types of small and bigger-than-medium-size unmanned aerial vehicles," the official noted. 

Roughly seven or eight drone missions are being detected by South Korea's surveillance system every day, according to other military sources.

The South Korean military is trying to determine the reason for the rise in drone exercises and stepping up its own surveillance over the area, the official said. 

"These drones may possibly cross over to our side of the demarcation line unexpectedly to confuse our military's combat readiness," the official said. "Or they could divert attention to the western front so as to allow the North to create problems elsewhere." 

According to other military officials, "The North Korean drones have not trespassed on the Military Demarcation Line, but the military has stiffened its surveillance for the possibility of infiltration." 

South Korea is seeking an aerial defense network that can detect and shoot down North Korean drones since the country has been steadily conducting drone exercises, Moon Sang-gyun, spokesman of the defense ministry, said during a press briefing. 

The military is mobilizing anti-aircraft radar and observation posts in its surveillance of North Korean drones, Moon said, indicating that the military will respond with Vulcan automatic cannons if any drones come over to South Korea.

Seoul already said it is in the process of upgrading its low altitude radar system to better pick up drones.

North Korea is reportedly operating some 300 UAVs, including those that specialize in reconnaissance and assault missions. Some of the drones may have come from China. 

Pyongyang has occasionally flown drones into South Korea in recent years, with some of them accidentally crashing into South Korean soil.

In the latest reported case, one North Korean drone briefly infiltrated the inter-Korean border on Jan. 13 before being steered back after being fired upon by the South. (Yonhap)