At Oil Port, Libya Air Strikes Hit Rebels.

TRIPOLI, Libya (AP) - After dramatic successes over the past weeks, Libya's rebel movement appears to have hit a wall of overwhelming power from loyalists of Moammar Gadhafi. Pro-regime forces halted its drive on Tripoli with a heavy barrage of rockets in the east and threatened Tuesday to recapture the closest rebel-held city to the capital in the west.

If Zawiya, on Tripoli's doorstep, is ultimately retaken, the contours of a stalemate would emerge -- with Libya divided between a largely loyalist west and a rebel east as the world wrestles with the thorny question of how deeply to intervene.

President Barack Obama and British Prime Minister David Cameron agreed to plan for the "full spectrum of possible responses" on Libya, including imposing a no-fly zone to prevent Gadhafi's warplanes from striking rebels. According to a White House statement, the two leaders spoke Tuesday and agreed that the objective must be an end to violence and the departure of Gadhafi "as quickly as possible."

Zawiya, a city of 200,000, was sealed off under a fifth day of a destructive siege, with conflicting reports of who was in control. A brigade led by one of Gadhafi's sons, Khamis, is believed to be leading the assault, shelling neighborhoods with tank and artillery fire from the outskirts and trying to push troops in to the city's central Martyrs Square where rebels had set up camp.

The city hospital has been overwhelmed with dead and wounded and many houses have been damaged, according to residents who escaped the past two days. One man who slipped out of the city on Monday said pro-Gadhafi forces had seized the central square.

An adviser to the Libyan Foreign Ministry in Tripoli on Tuesday also claimed that government troops were in control, raising the green flag over the square. The adviser, who is originally from Zawiya, said he was trying to mediate a cease-fire with remaining rebels. He spoke on condition of anonymity because of the sensitivity of the talks.

But a resident of the nearby town of Sabratha said people who fled from Zawiya on Tuesday afternoon told him fighting continued, with rebels back in control of the square. He said they reported hit-and-run attacks between the two sides.