North Korea may stage provocations against South Korea early next year as part of efforts to further ensure internal unity following the execution of leader Kim Jong-un's once-powerful uncle and his associates, a Seoul think tank said Tuesday.

   The North executed Jang Song-thaek on charges of treason, along with other officials in early December. The shocking series of purges sparked concerns over potential instability in the isolated country. 

   "There is a possibility that the North could attempt provocations at a time when the defense posture is slackened right after the end of military exercises," between South Korea and the United States, said the Institute for National Security Strategy, which is run by the National Intelligence Service.

   South Korea and the United States usually hold annual joint military exercises in March. The U.S. keeps about 28,500 troops in South Korea as a deterrent against the North.

   The institute also said the North may carry out cyber attacks on South Korea as it may be cautious about armed confrontations.

   There has been a spate of hacking attacks on South Korea in recent years that are blamed on the North.

   Seoul government officials have also been voicing similar concerns of a possible attack by North Korea.

   South Korean Defense Minister Kim Kwan-jin said the North may launch provocations between late January and early March as hardliners may try to demonstrate their loyalty to the young leader Kim Jong-un.

   North Korea has a track record of carrying out provocations at a time of its internal instability in an apparent attempt to divert people's attention and forge unity.

   South Korean President Park Geun-hye has ordered the military to beef up its vigilance against the North's possible provocations.

   Adding to the tensions on the Korean Peninsula, the North has posted some 60 attack helicopters and multiple rocket launcher systems near the inter-Korean maritime border in the Yellow Sea off the west coast.

   The poorly marked sea border, which the North has refused to recognize, has been the scene of a series of bloody naval clashes between the two Koreas. North Korea sank a South Korean warship near the sea border in March 2010 and shelled a border Island eight months later, killing a total of 50 South Koreans, mostly soldiers.

   Seoul has since beefed up defense posture and repeatedly vowed to retaliate against any provocations to avenge its people's deaths.

   In December, North Korea again threatened to strike South Korea, this time in anger over a Seoul rally, in which conservative protesters burned effigies of Kim and his father and grandfather, the North's two late leaders, Kim Jong-il and Kim Il-sung.

   The South Korean capital city of Seoul, with more than 10 million people, is within the range of North Korea's conventional artillery positioned along their heavily fortified border. (Yonhap News)