Libyan opposition forces have reportedly captured several residential districts of Brega, a strategic city for Muammar Gaddafi's government.
Speaking on Thursday, Mossa Mahmoud al-Mograbi, a spokesman for the opposition forces, said: "It is liberated. It is under our control now."
Sources told Al Jazeera that the opposition forces had suffered 40 casualties, including seven dead. They also said that 12 Gaddafi soldiers had surrendered.
Brega's western half, where its oil facilities are located, remains in the control of Gaddafi's forces.
Opposition forces hope that if they are able to take complete control of the city its oil terminal and sea port will allow them to resume oil exports.
Al Jazeera's Andrew Simmons, reporting from Misrata, called the opposition forces advances "very important and very significant".
Simmons said "it's definitely a move forward", but whether or not these gains remain is "subject to securing areas" and if "there's going to be a counter-offensive".
An area south of Brega was also captured by the opposition forces on Thursday, though clashes are ongoing.
"We are sure we will defeat them," said Mograbi.
The gains in Brega come as Libyan opposition forces continue their push north toward the town of Zawiyah.
Their aim is get within striking distance of Tripoli, the nation's capital and headquarters of Gaddafi.
The embattled leader has clung to power despite five months of NATO air strikes, suffocating economic sanctions and an expanding war with opposition forces.
PHOTO CAPTION
Libyan opposition forces fight forces loyal to Libya's leader Moamer Kadhafi in Bir Ghanam, 80 kilometers (50 miles) southwest of the Libyan capital Tripoli on August 6, 2011.
Al-Jazeera