Fresh fighting breaks out in South Sudan as renegade forces try to retake the key town of Bor

A South Sudanese military official says fighting erupted Tuesday morning in Bor, the contested capital of Jonglei state, as rebel forces tried to retake the strategic town held by government troops.

Military spokesman Col. Philip Aguer said Tuesday that government troops were fighting renegade forces loyal to former Vice President Riek Machar as well as a pro-Machar tribal militia known as the "White Army."

Regional leaders last week set Tuesday as the deadline for President Salva Kiir and Machar to start peace talks, and on Monday Uganda's president warned that neighboring countries would unite to "defeat" Machar if he doesn't stop his rebellion. Machar has called for a negotiated cease-fire.

South Sudan has been hit by unrest since Dec. 15, when fighting among presidential guards later spiraled across the country.