Hundreds of fighters were on the move along the road from the mountain town of Yafran toward the front lines, where heavy fighting seemed to be under way. The ground reverberated with loud booms and rocket fire echoed from the distance.
Their first objective was the town of Bir Ghanam, about 18 miles (30 kilometers) north of Yafran. As fighting raged there, the body of one rebel fighter killed earlier in the morning was brought back to the nearby town of Bir Ayad.
The rebel forces are aiming to "first liberate Bir Ghanam" and then would move on Zawiya, a key city on the Mediterranean coast 30 miles (50 kilometers) away, said two rebel fighters, Jumma Hussein and Youssef Bilin.
"We have thousands of fighters involved," Hussein said.
The assault is an attempt to open a new front and break the military deadlock that has emerged in Libya's civil war.
Gaddafi's regime controls much of the west, with its stronghold in Tripoli, while the rebels hold the east, with pockets in the west, including the Nafousa Mountains where Yafran is located and the city of Misrata on the coast, east of the capital.
But neither side has made significant gains for months. A NATO bombing campaign directed against government forces is now in its fifth month, but has so far failed to help the poorly-equipped rebels advance far beyond their strongholds. Libya's civil war erupted shortly after anti-regime protests swept across Libya in mid-February.
The new assault in the west would push right into the heartland of Gaddafi's control, a tough proposition. Zawiya, the rebel's main target on the coast, was the scene of a major uprising by protesters early on in the conflict. The protesters took over the city and drove out Gaddafi's supporters, but then were brutally crushed in a long, bloody siege.
Earlier this week, the rebels said they hope to reach the Libyan capital before the end of the Muslim fasting holy month of Ramadan, which began on Monday, at the end of August.
Saturday's offensive seems to be part of that effort but the rebels also appear to be aiming for smaller towns first, in a more phased and piecemeal push to Tripoli.
At the hospital in Yafran, two wounded rebels were brought in Saturday, one with a large caliber bullet injury to the arm.
Rebel fighter Moussa Hneish told The Associated Press that about 500 of his troops were fighting along two frontlines in the area, and that the rebels were aiming for Zawiya and another coastal town, Sabratha.
Hneish said that on the road to Sabratah, they were surrounding an unknown number of Gaddafi's forces and trading tank fire.