TRIPOLI, Libya — In the heaviest attack yet on the capital since the start of the two-month-old NATO bombing campaign, alliance aircraft struck at least 15 targets in central Tripoli early Tuesday, with most of the airstrikes concentrated on an area around Col. Muammar el-Qaddafi’s command compound.

The strikes, within a 30-minute period around 1 a.m., caused thunderous explosions and fireballs that leapt high into the night sky, causing people in neighborhoods a mile or more away to cry out in alarm.

Just as one strike ended, the sound of jet engines from low-flying aircraft in the stormy skies above the capital signaled the imminence of another. Huge plumes of black smoke rose and converged over the darkened cityscape.

“We thought it was the day of judgment,” one enraged Libyan said.

The intensity of the attacks, and their focus on the area of the Bab al-Aziziya command compound in central Tripoli, appeared to reflect a NATO decision to step up the tempo of the air war over the Libyan capital, perhaps with a view to breaking the stalemate that has threatened to settle over the three-month-old Libyan conflict.