Thailand said its navy joined the army in repelling Cambodian attacks along the border, as fighting spread to new areas on the third day of a conflict that has killed more than 30 people.

The naval operation early on Saturday followed the incursion of Cambodian troops at three different points in Trat province in Thailand’s east, the Thai Defense Ministry said in a statement. The marine forces’ counter-operation was able to push back Cambodian soldiers encroaching on Thai territory, it said.

Cambodia in turn accused Thai forces of expanding its offensive deep into its territory against non-military targets including schools, pagodas and residential areas. Thai forces fired heavy artillery shells into several Cambodian areas outside the conflict zone, the Khmer Times reported, citing its defense ministry spokesperson Maly Socheata. Thailand has denied targeting non-military sites.