Sri Lanka's army sank a Tamil Tiger rebel boat Wednesday in a three-hour artillery and mortar attack on a group of the insurgents' vessels off the east coast, the military said. It was not immediately clear whether there were any casualties. The fighting began about midnight when 15 to 20 rebel boats tried to land near Pulmoddai village, said a military spokesman, Brig. Udaya Nanayakkara. Soldiers on the shore destroyed one boat with artillery and mortar barrages, and eventually forced the other boats to turn back, Nanayakkara said. The rebels maintain a significant navy that they use for attacks and for smuggling weapons into areas they control.