NATO jets on Sunday already began enforcing the no-fly zone, Secretary-General Anders Fogh Rasmussen announced. Diplomats said the full transfer of authority would take several days.

"NATO allies have decided to take on the whole military operation in Libya under the U.N. Security Council resolution," Fogh Rasmussen said in a statement. "NATO will implement all aspects of the U.N. resolution. Nothing more, nothing less."

The North Atlantic Council — the alliance's top body — took two hours to approve a plan to expand a previously agreed mission to enforce the U.N. arms embargo and no-fly zone. It agreed to protect civilians from attack — which effectively means bombing Gadhafi's forces if they are threatening to harm the civilian population.

The U.N. authorized the operation after Gadhafi launched attacks against anti-government protesters who demanded that he step down after 42 years in power

"In the past week, we have put together a complete package of operations in support of the U.N. resolution by sea and by air," Fogh Rasmussen said.

After eight days of strikes on Libyan targets, Washington is eager to quickly hand off responsibility for the air offensive to the alliance. President Barack Obama and U.S. Defense Secretary Robert Gates have both said that American command of the military operations in Libya would last only a few days.

Gates has said that major strides are being made in bolstering rebels, but acknowledged the international operation could drag on for months. NATO officials said the alliance's operations, approved for up to three months, could be extended if necessary.