The United Nations Security Council voted Thursday to approve a resolution authorizing international military intervention in Libya to protect civilians from harm.

Forces loyal to Col. Muammar Qaddafi have been overrunning one opposition stronghold after another and are close to crushing the rebellion that has threatened his 41-year reign. Now the rebels have the backing of the international community, including the United States, if it is not too late.

The resolution, which was drafted by France, Britain, and Lebanon, goes beyond a no-fly zone. It authorizes states to take “all necessary measures” to enforce a ban on flights and protect civilians from harm. That could include targeted air strikes on Libyan military forces, but excludes a ground invasion or occupation force. The resolution passed by a vote of 10 to 0, with five nations abstaining: Russia, China, Germany, India, and Brazil.

Initially, the United States was reluctant to support even just a no-fly zone over Libya, until the Arab League came out in support of one last Saturday. Once an international consensus began to form, the US did an about-face. In deliberations at the UN, the Obama administration had called for the authority to use force by land, sea, and air, on the condition that Arab governments be centrally involved.

Speaking in Tunisia, Secretary of State Hillary Rodham Clinton said Thursday that a no-fly zone would include “certain actions taken to protect the planes and the pilots, including bombing targets like the Libyan defense systems.”

“Qaddafi must go,” she added.

The Security Council voted as Mr. Qaddafi’s forces prepared for a major offensive against the rebel stronghold of Benghazi in eastern Libya. Thursday evening, Qaddafi went on state television and warned rebel forces, “We are coming tonight.”

Even as the Security Council took action, concerns grew that the measure was too late to stop Qaddafi from fully reasserting control over the country.

France, however, insisted it was not too late. Its prime minister said action could come within hours of the vote, according to the Associated Press.

And in Benghazi itself, the mood shifted in an instant to one of triumph as the Libyan opposition lit up the sky with celebratory gunfire within 2 minutes of the resolution passing.