NATO aircraft have launched round-the-clock surveillance patrols of Libya's air space to track Muammar Gaddafi's air force as he battles opposition forces, an alliance official said.

The move comes as NATO defense ministers meet Thursday to weigh a possible no-fly zone against Gaddafi's regime.

With the sophisticated, radar-equipped aircraft monitoring Libya's skies, "we'll have a much better picture and that will help inform the discussions that will take place in Brussels today," the NATO official, who spoke on condition of anonymity, told AFP.

"It's not a precursor to a no-fly zone," the official added.

After a decision announced earlier by NATO, at least three airborne warning and control system (AWACS) planes -- modified Boeing 707s -- started 24-hour surveillance as of Thursday at 6:30 am, the official said.

"Now they've got enough aircraft in place operating out of Trapani in southern Italy to be able to cover that part of the world on a 24/7 basis," said the official.

"The AWACS provides us with first-hand information about air activity, predominantly, because all we've had to go on is reports of the use of air power," the official said.

He added, however, that media reporting on bombing raids by Gaddafi's aircraft "seems fairly compelling."

The AWACS planes, flying out of a base in Trapani in southern Italy, were previously operating in the Mediterrean for NATO counter-terrorism surveillance efforts.