(AP) — Opposition forces pushed back an attack by the Libyan dictator’s forces trying to retake a key coastal oil installation in a topsy-turvy battle Wednesday in which shells splashed in the Mediterranean and a warplane bombed a beach where rebel fighters were charging over the dunes. At least five people were killed in the fighting.

The assault on the Brega oil port was the first major regime counteroffensive against the opposition-held eastern half of Libya, where the population backed by mutinous army units rose up and drove out Gaddafi’s rule over the past two weeks.

The Gaddafi forces initially re-captured the oil facilities Wednesday morning. But then a wave of opposition citizen militias drove them out again, cornering them in a nearby university campus where they battled for several hours until the approximately 200 Gadhafi loyalists fled, according to an Associated Press reporter at the scene.

Soon after sunrise Wednesday, a large force of Gaddafi loyalists in around 50 SUVS, some mounted with machine guns, descended on opposition-held Brega, 460 miles (740 kilometers) east of Tripoli along the Mediterranean. The force caught a small opposition contingent guarding the site by suprise and it fled, said Ahmed Dawas, an anti-Gaddafi fighter at a checkpoint outside the port.

The pro-Gaddafi forces seized the port, airstrip and the oil facilities where about 4,000 personnel work, as regime warplanes hit an ammunition depot on the outskirts of the nearby rebel-held city of Ajdabiya, witnesses said.

Midmorning, the opposition counter-attacked. Anti-Gaddafi fighters with automatic weapons sped out of Ajdabiya in pickup trucks, heading for Brega, 40 miles away (70 kilometers) away. Dawas said they retook the oil facilities and airstrip. Other witnesses reported regime forces were surrounded by rebels. The sound of screaming warplanes and the crackle of heavy gunfire could be heard as the witnesses spoke to The Associated Press by phone.

By the afternoon, the regime fighters fled the oil facilities and holed up in a nearby university campus, where they came under siege by anti-Gaddafi fighters, according to an Associated Press reporter at the scene.

Machine gun and automatic weapons fire rattled in the air, and shells lobbed from the campus went over the anti-Gaddafi side to splash in the Mediterranean.

At one point, a warplane from Gaddafi’s airforce swooped overhead and an explosion was heard. A witness said it struck an empty stretch of dunes near the battle, sending a plume of sand into the air but causing no injuries in an apparent attempt to intimidate the anti-Gaddafi side.

But opposition citizen militias poured into the battle, arriving from Ajdabiya and armed with assault rifles. They moved through the dunes along the beach against the campus next to a pristine blue-water Mediterranean beach. Those without guns picked up bottles and put wicks in them to make firebombs.

At least five opposition fighters were killed in the fighting, their bodies covered with sand thrown up by shells bursting in the dunes. Angry crowds gathered around them at Brega’s hospital, chanting, “The blood of martyrs will not go in vain.”

In the late afternoon, the pro-Gaddafi force fled the campus, and opposition fighters were seen combing through the university buildings. Automatic gunfire was still heard in the distance, but it appeared the regime troops were withdrawing. The campus grounds and dunes between it and the beach were littered with casings and shells.

In Ajdabiya, people geared up to defend the city, fearing the pro-Gaddafi forces would move on them next. At the gates of the city, hundreds of residents took up positions on the road from Brega, armed with Kalashnikovs and hunting rifles, along with a few rocket-propelled grenade launchers. They set up two large rocket launchers and an anti-aircraft gun in the road. But by the evening, there was no sign of attack there.

Brega and nearby Ajdabiya are the furthest west points in the large contiguous swath of eastern Libya extending all the way to the Egyptian border that fell into opposition hands in the uprising that began Feb. 15. Ajdabiya is about 90 miles (150 kilometers) from Benghazi, Libya’s second largest city and the nerve center of the opposition.