The battle in the northeast of the island nation marked the eighth day of heavy fighting between the two sides for control of an irrigation waterway in the Trincomalee area despite a truce in place since 2002.
The Tigers also fired mortar bombs early Wednesday at troops near an irrigation canal, wounding six people, including two civilians, local officials said.
Military officials said the Liberation Tigers of Tamil Eelam (LTTE) launched attacks on three military camps overnight in the southern sector of Trincomalee where they had targeted the main naval port Tuesday, military officials said.
The army said it had suffered no casualties and the rebels did not immediately comment, but medical sources said at least 20 civilians had been wounded after being caught up in the cross fire.
"There are 20 civilians admitted," a doctor at the main Trincomalee hospital said.
"We have asked for Red Cross help to evacuate these people."
The Tigers attacked the Kattaparichchan army camp and two of i