TOBRUK, Libya >> Moammar Gadhafi’s air force bombed the airport in the Libyan opposition’s main stronghold today after the rebels used seized planes and helicopters to launch attacks on the government’s advancing troops, witnesses and rebel officials said.

Two planes bombed Benina airport just outside the city of Benghazi, one witness told The Associated Press. The extent of the damage was not immediately clear.

The rebels were using three of their own planes and some helicopters to attack Gadhafi’s troops outside the city of Ajdabiya, the gateway to Benghazi and surrounding opposition-held territory, said Mustafa Gheriani, an opposition spokesman in Benghazi.

Witnesses and rebels said Gadhafi’s forces had surrounded Ajdabiya, seizing positions on all sides of the rebels, who are hoping for help from the U.N. Security Council before government troops move in.

The two sides have been fighting hard in Ajdabiya and a senior hospital official told The Associated Press that 30 people had been killed and at least 80 wounded since Tuesday night. Many more of the injured couldn’t reach the hospital, according to the official there, who spoke on condition of anonymity for fear of official retaliation.

Gadhafi’s rapid advance on the rebels appears to have spurred the United States to leave behind weeks of doubts about a no-fly zone in Libya, and start advocating for broader U.N. authorization for international air, sea and land forces.

The Obama administration and other supporters of action against Gadhafi were pushing for a vote today on a draft resolution. Russia and China have expressed doubts about the U.N. and other outside powers getting involved.

By Thursday afternoon, Gadhafi’s army had were on three sides of Ajdabiya, leaving open only the road north to the larger rebel stronghold of Benghazi.

Government forces also seized the nearby port town of Zwitina, which sits off that northern road, giving Gadhafi positions encircling Ajdabiya, activist Abdel-Bari Zewi told the AP.

He said that a fierce battle at the southern gates of Ajdabiya erupted just after midnight and lasted nearly three hours.

“The rebels appear only at night, not in the morning,” he said. “When we woke up this morning, we found Gadhafi’s troops still there.”

Zewi said the rebels, who officials have said control at least three planes, launched airstrikes against Gadhafi’s troops about 10 miles from the western gate of Ajdabiya.

“Gadhafi troops have not invaded the city on foot until now,” said Moataz al-Ghariani, who lives in downtown Ajdabiya and is in touch with the rebels. “They are only imposing a siege from three fronts: the western, the southern and the eastern. No one can leave and no one can enter.”

Ajdabiya is the last major city on the road to the main rebel stronghold of Benghazi, 100 miles to the north along the Mediterranean coast.

Gheriani, the rebel spokesman, said by telephone from Benghazi that the opposition was hoping for a positive U.N. Security Council vote but “if not, we’ll rely on ourselves and do what we can.”

Gheriani told The Associated Press that Benghazi was “armed to the teeth” and the opposition is ready to defend it.

More checkpoints were popping up at intersections and on main roads in Benghazi, manned by men in uniform armed with Ak-47s and backed by anti-aircraft guns mounted on pickup trucks.

A Benghazi resident who did not want to be identified for fear of reprisals said the city’s young men were volunteering to undergo basic military training. Those already trained were seeking more preparation to be battle ready.

Gheriani said that the government tried to hit Benghazi’s airport with an airstrike Thursday but missed.

The Red Cross said it was leaving Benghazi because of deteriorating security and moving to the city of Tobruk, further east.

The U.S. wants the Security Council to approve planes, troops or ships to stop attacks by Gadhafi on the rebels, according to a diplomat familiar with closed-door negotiations Wednesday.

The Obama administration said it would not act without Security Council authorization, did not want to put U.S. ground troops into Libya, and insists on broad international participation, especially by Arab states, the diplomat said.