BENGHAZI (AFP) - The battle for the oil town of Brega switched from the desert to intense street fighting in the town's northeast on Sunday, as veteran Libyan leader Moamer Kadhafi vowed never to quit and fresh blasts rocked Tripoli. Rebel forces re-entered Brega - putting them within sight of a major strategic victory - but said they had not yet managed to wrest control of the town from Kadhafi's troops, who have held it since April. "Some small groups have made it inside, but we do not control the whole (town) yet," said Mohammed Zawi, a spokesman for the rebel forces. He also dismissed rumours that Kadhafi troops had abandoned the town altogether. "It is now close fighting," he said, indicating a new phase in the four-day rebel campaign. Until now heavy artillery had set the tenor of the battle, but mortars and rockets appear to have given way to heavy machine guns - a more useful weapon for fighting at closer quarters. But that did little to stem the bloodshed. Some 13 rebel fighters have now been killed and almost 200 wounded since the battle for Brega began on Thursday. In Brussels, a NATO statement said its forces were monitoring "the dynamic situation across the country, including around Brega." Nestled on the Gulf of Sirte, Brega is made up of three areas, a residential area in the east, a major oil facility in the west and an old town in between. A small rebel force had entered Brega from the northeast late on Friday, before pulling back for NATO air strikes and for fellow fighters to the south to beat back Kadhafi's troops. After a series of military gains were washed away by hasty and badly coordinated advances, rebel commanders said they are anxious to make sure they have a unified offensive line before their final push. NATO's strikes continued on Saturday, with the alliance hitting a tank, five armed vehicles and two rocket launchers in the Brega area. A series of blasts rocked Tripoli on Sunday after Kadhafi vowed never to go into exile, with at least 13 explosions heard before and just after 01:00 am (2300 GMT Saturday). The NATO statement in Brussels said warplanes had hit "a large military vehicle storage area in Tajura, 30 kilometres east of Tripoli.