Rebel Serbs recalled soldiers from leave Tuesday, and the government appeared to be reinforcing its positions around Sarajevo, tense already from fatal weekend sniping.

The government was building up infantry and artillery on at least two major fronts outside the capital, said a senior Serb military official in Pale, the Bosnian Serb headquarters south of Sarajevo. He spoke on condition of anonymity.

He said the Bosnian government army’s 1st Corps has moved its field hospital to the edge of a demilitarized zone on Mount Igman, a strategic peak near Sarajevo.

Bosnian government forces have been digging a fresh trench around the government-held suburb of Hrasnica, at the foot of Mount Igman, for the past week, U.N. spokesman Lt. Col. Gary Coward said.Grlica, where two Serbs died in sniper attacks during the weekend, is a Serb-held suburb adjacent to Hrasnica.

Coward said U.N. officials saw tracks indicating that Bosnian government soldiers had moved through the demilitarized zone on Mount Igman to bolster positions to the east.