The head of South Korea's spy agency says he believes further attacks from the North are highly likely.
North Korea shelled the island of Yeonpyeong on 23 November, killing at least four South Koreans; two marines and two civilians.
National Intelligence Service director Won Sei-hoon is reported to have told MPs that the shelling was linked to attempts to install Kim Jong-Il's third son as the North's next leader.
According to a ruling party official, he said the attacks came amid "internal complaints" about the succession in Pyongyang and a worsening economic situation.
The Yonhap news agency quoted Won as saying: "There is a high possibility that the North will make another attack."
South Korea says it wants more joint military exercises with the United States off the western coast of Korea.
The BBC reports China has urged all parties to avoid further escalating tensions on the Korean peninsula.
Beijing has also been pressing for a resumption of the six-nation talks on ending North Korea's nuclear programme.
The United States has said these talks cannot resume until North Korea apologises for its torpedoing of a South Korean warship in March, and stops further nuclear enrichment plants from operating.