South Korean President Lee Myung-bak accepted the resignation of his defence minister on Thursday, two days after an attack by North Korea and amid criticism that the South's response was too slow.
Minister Kim Tae-young had tended his resignation in May after criticism over the sinking of a South Korean naval vessel, the Cheonan, in March, also blamed on North Korea. Forty-six South Korean sailors were killed in the attack.
Lee only accepted the resignation on Thursday "to improve the atmosphere in the military and to handle the series of incidents", a presidential official said.
North Korea fired a barrage of artillery shells at island of Yeonpyeong off the peninsula's west coast on Tuesday, killing two civilians and two soldiers and destroying dozens of houses. Members of Lee's own party and opposition lawmakers accused the military of responding too slowly.
The government was also criticised for its perceived weak response to the Cheonan incident. North Korea has denied responsibility for that attack.
China on Thursday expressed muted concern about joint U.S.-South Korean military exercises in the Yellow Sea, while North Korea threatened further attacks on the South if there were more "provocations".
Seoul said it would increase troops on islands near North Korea after the bombardment, which caused a sharp spike in tension in the world's fastest growing region.
Washington is putting increasing pressure on China to rein in North Korea, but a foreign ministry spokesman in Beijing said what was needed was a revival of the stalled six-party talks involving the two Koreas, Russia, China, Japan and the United States.
"We have noted the relevant reports and express our concern about this," spokesman Hong Lei said, referring to the joint military exercises next week and the involvement of the nuclear-powered aircraft carrier the USS George Washington in the drill.
But Beijing has previously used stronger language to signal its displeasure. In August, the People's Liberation Army said earlier plans to send the George Washington to the Yellow Sea would make it lose respect and threatened long-term damage to Sino-U.S. relations.
Seoul expressed frustration with Beijing for not taking sides, noting even Russia had condemned this week's attack.
"We must engage with China for it to take more responsibility on North Korea's behaviour," a government official, who asked not to be named.