"From our side 18 soldiers were killed and some 35 others wounded," Sarkisian said in a televised statement.
He did not specify if the soldiers belonged to Yerevan-backed separatist forces in Karabakh or Armenia's armed forces.
Earlier today Azerbaijan's defence ministry said that 12 its soldiers were killed in Karabakh and a military helicopter was shot down.
The surge in fighting over the disputed territory -- which separatist Armenian-backed forces captured from Azerbaijan in the early 1990s -- reportedly also claimed the lives of one Armenian and one Azeri civilian after the arch foes accused each other of unleashing heavy weaponry across the volatile frontline.
The two sides frequently exchange fire across the front but the latest episode has marked a surge in violence and sparked appeals for peace from international powers.