TRIPOLI, Libya — Heavy anti-aircraft fire is lighting up the skies over Tripoli and the sound of loud explosions is echoing through the Libyan capital after nightfall.

The gunfire appeared to signal a fourth night of U.S. and
European air operations over Libya to enforce a no-fly zone.

In the previous night's operations, the coalition air campaign suffered
its first loss with the crash of an American fighter jet in the
rebel-held east. Both crew ejected safely as the aircraft spun from
the sky.

The no-fly zone is intended to protect civilians from attack by
forces loyal to Moammar Gadhafi in their battles with rebel
fighters. The uprising against Gadhafi's four-decade rule began
Feb. 15.
 

The international air campaign over Libya has hobbled Moammar
Gadhafi's forces, but they continue to strike rebel positions on
two fronts.
 

Ajdabiya (ahj-DAH'-bee-yah) is considered the gateway to the
east, and Gadhafi's forces have been laying siege to it for a week.
A ragtag group of rebel fighters is coming under artillery attacks
from Gadhafi loyalists inside the city.
 

Gadhafi's troops and tanks also have been roaming the last major
opposition-held city in western Libya.