"We are preparing to enter Brega. The attack will come soon" said one rebel official, adding that the offensive had been slated for Wednesday night but was delayed. The attack could come later on Thursday or early on Friday after rebels had set their positions, according to the sources, who asked not to be named.
"We will move in the coming hours and we shall soon be in Brega, God willing," said another official.
Brega, nestled at the southeastern tip of the Gulf of Sirte, has changed hands multiple times during Libya's civil war, which soon enters its fifth month. The town's vast oil refinery and storage facilities are just one reason for its strategic value.
Beyond the city are hundreds of kilometres (miles) of largely open desert before Libyan leader Moamer Kadhafi's home town of Sirte -- which lies just 360 kilometres (225 miles) from Tripoli and about 200 kilometres (125 miles) from the besieged rebel enclave of Misrata.
But while fighting has raged in the west in the Nafusa Mountains and around Misrata, there has been relative calm on the eastern front except for skirmishes and rockets occasionally slamming into civilian areas of Ajdabiya.
"We have been focused on the west of the country, but now we will move," said a third rebel military source who also asked not to be named.
There are thought to be only a handful of civilians left in Brega and on its outskirts, but it is home to between 2,000 and 3,000 troops loyal to Gaddafi.
Rebels in recent weeks have been holed up at a forward position 40 kilometres between Brega and Ajdabiya, inching forward and clearing mines so their handful of T-72 tanks and infantry fighting vehicles can have a freer rein.
Meanwhile NATO has been hitting whatever heavy pieces Gaddafi's troops have out in the open.
In rebel-held Ajdabiya on Wednesday there was some evidence of a military buildup, with heavier traffic heading toward the front than in recent weeks and guards furtively checking papers.
Most of the weapons being carried to the front were the familiar array of "technicals" -- pickup trucks fixed with anti-aircraft guns, machine guns and rocket launchers.
Meanwhile in the past 24 hours, NATO said it hit six targets in Brega: one command and control node, one tank and four armed vehicles.
Journalists have rarely been allowed to pass the checkpoint at the western gate of Ajdabiya in recent months as rumours of an imminent offensive have swirled.