SEOUL (Reuters) - South Koreas marine commander on Saturday vowed thousand-fold revenge for a North Korean attack that killed two servicemen and two civilians and prompted an unusual expression of regret from North Korea. South Korean President Lee Myung-bak told ministers and aides to be ready for further provocation by North Korea during military maneuvers with the United States that start on Sunday. There is the possibility that North Korea may do some unexpected action, so please perfectly prepare against it through cooperation with the Korea-U.S. joint force, Lee was quoted by a spokesman as saying. The two marines were honored with a gun salute as families wailed and grim-faced officials saluted the funeral cortege, four days after North Korea rained shells on a tiny island in the heaviest attack on South Korea since the 1950-53 civil war. North Korea, not known for agonizing over policy decisions, said if there were civilian deaths, they were very regrettable, but that South Korea should be blamed for using a human shield. It also said the United States should be blamed for orchestrating the whole sequence of events to justify sending an aircraft carrier to join the maritime maneuvers. Dozens of houses were destroyed in the attack, which followed South Korean test firing near disputed waters. South Korea responded with artillery fire 13 minutes later, but it was not clear what damage was caused. All marines, including marines on service and reserve marines, will avenge the two at any cost, keeping todays anger and hostility in mind, said Lieutenant General Yoo Nak Joon, commander of the South Korean Marine Corps. We will put our feelings of rage and animosity in our bones and take our revenge on North Korea. The funeral was followed by anti-North Korea protests in the capital as a U.S. aircraft carrier headed for the maneuvers with South Korea, infuriating North Korea and prompting a warning from its only major ally, China. Its time for action. Time for retaliation. Lets strike the presidential palace in Pyongyang, shouted close to 1,000 marine veterans in downtown Seoul, who burned photographs of North Korean leader Kim Jong-il and his anointed successor, his son Kim Jong-un. Veterans of an underwater sabotage team protested against North Korea and accused the government of disregarding their sacrifices on spy missions. Scuffles broke out and police used fire extinguishers to break up the crowd. Regional giant China under pressure from other powers to rein in North Korea has said it is determined to prevent an escalation of the violence. But it warned against military acts near its coast as U.S. and South Korean forces prepare for exercises in the Yellow Sea. China sent senior officials including State Councillor Dai Bingguo to Seoul for an unscheduled meeting with South Korean Foreign Minister Kim Dung-hwan, Seoul said. There was no immediate word on what had been discussed. Japanese Foreign Minister Seiji Maehara and his Chinese counterpart, Yang Jiechi, spoke on the phone on Saturday and affirmed that Japan and China would work to try to avoid further tension on the Korean peninsula, Kyodo news agency said. We hope that China will show strong leadership so that North Korea will not undertake further actions, Kyodo quoted Maehara as telling Yang. North Koreas bellicose KCNA news agency said South Korea had formed a human shield around artillery positions and inside military facilities and was to blame for any civilian deaths. If the U.S. brings its carrier to the West Sea of Korea at last, no one can predict the ensuing consequences, it said. Kim Yong-hyun, a professor of North Korean studies at Dongguk University in Seoul, said North Korea had had no choice but to express regret about the civilian deaths. If it didnt, it would face heavy pressure from the whole international community, he said. Still, it is difficult to find sincerity if we read the whole statement. The U.S. military said the exercises, planned long before Tuesdays attack, were designed to deter North Korea and were not aimed at China. Weve routinely operated in waters off the Korean peninsula for years, said Captain Darryn James, a Pentagon spokesman. These latest provocations have been by the North and they need to take ownership of those, not us.