Pakistani fighter jets flew low near major cities on Monday amid tensions with India triggered by last month's terror attacks on Mumbai.
The air force declined to comment on the flights but issued a statement saying that "in view of the current environment, the Pakistan Air Force has enhanced its vigilance."
The apparent exercises briefly delayed two Pakistan International Airlines flights, said a spokesman for the airline. Several jets were seen flying close to Lahore and Islamabad, alarming some residents, witnesses said.
Last weekend, Pakistan said Indian jets violated its airspace in two parts of the country, but were chased back over the border. New Delhi said there was no violation.
Nuclear-armed India and Pakistan have fought three wars over the last 60 years.
India accuses Pakistani militants of planning and carrying out the attacks on Mumbai. Pakistan has promised to cooperate, but the strikes have raised tensions nevertheless.