Libyan rebels say they have been forced to pull back from the key oil port of Ras Lanuf, after forces loyal to leader Moammar Gadhafi closed in on the town.
News reports said intense fighting was underway in the area Wednesday, with pro-government forces heavily shelling the rebels and firing rockets.
The reports said large numbers of rebels fled east in pickup trucks.
On Tuesday, pro-Gadhafi troops reversed a westward push by anti-government forces, hammering them with tank and artillery fire and forcing a panicked retreat to Ras Lanuf. Opposition fighters pleaded for allied air strikes as they fled.
Pro-Gadhafi forces reached the outskirts of Ras Lanuf by late Tuesday, where heavy weapon fire could be heard.
Loyalist troops also continued to besiege Misrata, the last significant rebel holdout in the west. A rebel leader in Libya's third-largest city said Tuesday that Gadhafi's forces were "firing randomly" into the opposition-controlled center from the perimeter and along the one government-controlled thoroughfare.
An opposition spokesman said pro-Gadhafi forces were expelling families from their homes in Misrata and that the situation was very dangerous. The U.S. Navy reported two of its aircraft and a guided missile destroyer attacked a number of Libyan coast guard vessels in the Misrata port late Monday to prevent them from shelling merchant ships.
A series of loud explosions also rocked Tripoli Tuesday, and state television said several targets in the Libyan capital had come under attack - the first time such strikes have occurred in daylight hours.
Meanwhile, in Washington, U.S. Admiral James Stavridis told a congressional hearing that intelligence reports suggest "flickers", low levels, of possible terrorist involvement among Libyan rebel forces, but no evidence of significant numbers.
The NATO Supreme Allied Commander in Europe said groups such as al-Qaida and Hezbollah have a small presence among the Libyan opposition.
The rebels deny any al-Qaida links and Tuesday promised free and fair elections if Gadhafi is forced from power.
Western nations began enforcing a United Nations-authorized no-fly zone over Libya on March 19. On Wednesday, NATO member states will begin enforcing all military operations in the North African nation.
Some information for this report was provided by AP, AFP and Reuters.