A South Korean lawmaker presented North Korean rocket casings Thursday from the attack on a border island, pointing to the use of high-explosive weapons against civilian targets.

Park Sang-Eun, a lawmaker of the ruling conservative Grand National Party, presented the mangled and charred remains in front of TV cameras during a meeting of party leaders, saying he had picked up the debris on a trip to the island.

Seoul said the North fired up to 170 projectiles, of which 80 hit Yeonpyeong island, killing two marines and two civilians, injuring 18 more people, destroying about 20 homes and setting forests and fields ablaze.

Most previous official reports had referred only to artillery shells.

"Most of casings found on the island came from multiple rocket launchers," Park told journalists, according to his aide.

"Rockets fell on civilians homes, administrative offices and a medical centre, not only on military targets."

A multiple rocket launcher -- usually mounted on a truck or tank -- can, unlike a traditional artillery gun, fire many unguided rockets in fast succession, delivering a large explosive load almost instantaneously.

Park presented two casings fired from 122mm multiple launch rocket systems, saying he had found one near a military installation and the other in the backyard of the island's post office.

The 122mm rocket packs 27 kilograms (59.4 pounds) of powder, compared with the 3.6 kilograms of powder found in an ordinary artillery shell, the conservative Munhwa Daily said.