Fighting broke out in the Yemeni capital Wednesday between government forces and troops backing the pro-democracy movement, and at least one rebel soldier was killed.

The clash ensued after rebel troops marched down Sanaa’s main road toward the airport, setting up checkpoints as they continued to seize territory, and government forces were ordered to stop the defectors’ advance.

Demonstrators have been rallying across Yemen since February, demanding the resignation of President Ali Abdullah Saleh. But the fighting Wednesday was the first significant outbreak of violence between rival military factions since the defection last month of Maj. Gen. Ali Mohsen al-Ahmar, a political rival of Saleh’s. The embattled president has threatened “mutinous” military commanders that he would drag the country into a “long, bloody civil war” if they continue to support the pro-democracy demonstrators.

“We pray that there will be no more clashes with our fellow countrymen. However, if attacked again, we are committed to defending ourselves,” rebel Col. Abdul Salaam al-Aliyani said Wednesday.

Rebel soldiers have set up checkpoints and campsites along Sanaa’s main road, less than a mile from the country’s largest international airport. They have also positioned themselves near the state television station in the same area.

Mohsen’s largest military base in Sanaa is also located along this major highway, as is the base occupied by Saleh’s Republican Guard. The rival factions have set up camp within hundreds of yards of each other.

Abdul Rabo, 28, a mechanic with a shop along the road where the fighting took place, described the fierce firefight. “The two armies exchanged AK-47 and [rocket-propelled grenade] fire for at least an hour,” Rabo said. “I had to take cover behind a restaurant because I knew I would die if an RPG round hit my small house next to my shop.”

Yemeni political analyst Abdul Ghani al-Iryani said it is only a matter of time before Mohsen’s forces seize control of the airport and the state television station.

“The 1st Armored Brigade is postured to take both the airport and Yemen TV. Ali Mohsen sees these two strategic points as valuable bargaining chips,” Iryani said. “The two military factions do not want to fight each other, but at this point, there is no way to prevent further clashes between them.”

Also Wednesday, soldiers and riot police clashed with thousands of protesters in the southern city of Aden, killing at least one person, the Associated Press reported. Tens of thousands also protested in Sanaa in some of the biggest demonstrations in the country to date.

Boone is a special correspondent.