TOBRUK, Libya >>The U.N. Security Council approved a no-fly zone over Libya today and authorized "all necessary measures" to stop its leader Moammar Gadhafi — including strikes by sea and air — hours after he vowed in harrowing terms to launch a final assault and crush the weeks-old rebellion against him.

The resolution, approved with the backing of the United States, France and Britain, imposed a no-fly zone over Libya and authorized all measures short of a ground offensive to protect its people from Gadhafi’s forces.

The U.N. resolution bans all flights in Libyan airspace in order to protect civilians. While it was unclear how the West might proceed, U.S. Secretary of State Hillary Rodham Clinton said earlier in the day that a no-fly zone would require bombing targets inside Libya, including some of its defense systems.

It was also unclear when any Western action would come. A British lawmaker said British forces could be mobilized as early as Thursday night. U.S. officials, speaking after a closed-door briefing in Congress, said they expected an attempt to ground Gadhafi’s air force could begin by Sunday or Monday and would probably involve jet fighters, bombers and surveillance aircraft.

After deliberating for weeks over what to do about Gadhafi, the West acted with sudden speed as it became clear Gadhafi would attempt to finally put an end to the rebellion.

Gadhafi, calling in to Libyan television today, said his forces would "rescue" the people of Benghazi, the Mediterranean port city that has become the capital and staging ground for the opposition. For those who resist, Gadhafi said, there would be "no mercy or compassion."

"This is your happy day, we will destroy your enemies," he said, warning the people of Benghazi not to stand alongside the opposition. "Prepare for this moment to get rid of the traitors. Tomorrow we will show the world, to see if the city is one of traitors or heroes."

"Don’t betray me, my beloved Benghazi," he said.

His ground forces were still about 80 miles south of the city this evening Libya time, so it was unclear whether they would move on the city as quickly as he suggested.

Speaking moments before in an interview with Portuguese television broadcast just before the vote at the U.N., Gadhafi pledged to respond harshly to U.N.-sponsored attacks. "If the world is crazy," he said, "we will be crazy, too."

At the U.N. headquarters in New York, the vote was 10-0. The United States, France and Britain had all pushed for speedy approval. "We had said all along that Gadhafi must go," said British Foreign Secretary William Hague. "It is necessary to take these measures to avoid greater bloodshed."

Five nations abstained, including Russia and China, which hold veto power on the council.

In Washington, officials said the Obama administration was readying plans to enforce the no-fly zone. The French prime minister said before the measure was passed that his nation would support military action within hours. Several Arab nations were expected to provide backup.

"Today the Security Council has responded to the Libyan people’s cry for help," said Susan Rice, the U.S. ambassador to the U.N. "Colonel Gadhafi and those who still stand by him continue to grossly and systematically abuse the most fundamental of the human rights of his people."

The United States already has warships positioned near Libya. After eight hours of closed-door talks on Wednesday, Rice said a no-fly zone now was not enough, saying it has "inherent limitations in terms of protection of civilians at immediate risk."

In Britain, a lawmaker with knowledge of defense matters confirmed that British forces were on standby for air strikes and could be mobilized as soon as tonight. The lawmaker declined to be named because the Defense Ministry has not issued official confirmation.

French President Nicolas Sarkozy’s office issued a one-sentence statement at about 2 a.m. Friday Paris time saying he and Obama had spoken by phone about the resolution. Reached by The Associated Press, Sarkozy’s office declined further comment.

Western countries have significant military assets nearby, including carriers in the Mediterranean, a large U.S. air base in Italy and a large British air presence on the island of Cyprus. In addition, allied Arab countries such as Jordan and Oman have planes and pilots often trained by the U.S., and American officials have made clear they want active involvement by Arab countries if any action is taken.

The U.N. resolution specifically bans a ground offensive against Libya.

A large crowd in Benghazi was watching the vote on an outdoor TV projection and burst into cheers, with green and red fireworks exploding overhead. In Tobruk, east of Benghazi, happy Libyans fired weapons in the air to celebrate the vote.

Speaking to reporters in Tripoli after the vote, Libyan Deputy Foreign Minister Khalid Kaim struck a more conciliatory tone, offering to negotiate a cease-fire with the rebels. He welcomed the Security Council’s concern for the people of Libya but called on the world not to allow them to receive weapons. "If any countries do that, they will be inviting Libyans to kill each other," he said.

The shift toward international action reflected dramatic change on the ground in Libya in the past week. The rebels, once confident, found themselves in danger of being crushed by an overpowering pro-Gadhafi force using rockets, artillery, tanks, warplanes. That force has advanced along the Mediterranean coast aiming to recapture the rebel-held eastern half of Libya.

Gadhafi troops encircled the city of Ajdabiya, the first in the path of their march, but also had some troops positioned beyond it toward Benghazi.

Several witnesses said rebels in Benghazi succeeded in shooting down at least two of the attacking aircraft. Mohammed Abdel-Rahman, a 42-year-old merchant who lives nearby, said he saw one of the warplanes shot down after striking Benina, the airport.

Another witness, medical official Qassem al-Shibli, told The Associated Press that he saw three planes attack the airport and nearby rebel military camps before two were shot down. A third witness saw fire trucks fighting a blaze at the airport, and black smoke billowing from the area. Another witness reported that a rebel warplane crashed north of Benghazi, apparently after running out of fuel.

At the same time, the rebels were sending their own warplanes in an attempt to break the regime’s assault on Ajdabiya, a city about 100 miles southwest of Benghazi that has been under a punishing siege by Gadhafi’s forces the past two days. But by Thursday afternoon, Gadhafi’s army were holding the southern, eastern and western outskirts of Ajdabiya.

The unrest in Libya began Feb. 15 in the eastern city of Benghazi and spread east to Tripoli, the capital. Like others in the Mideast, the protest started with popular demonstrations against Gadhafi, rejecting his four decades of despotic and often brutal rule. The tone quickly changed after Gadhafi’s security in Tripoli forcefully put down the gatherings there.

Soon rebel forces began arming themselves, quickly taking control of the country’s east centered on Benghazi, the second largest Libyan city, with a population of about 700,000. Some Libyan army units joined the rebels, providing them with some firepower, but much less than Gadhafi’s remaining forces, and crucially, no air power.

There are no official death tolls. Rebels say more than 1,000 people have been killed in a month of fighting, while Gadhafi claims the toll is only 150.