ISLAMABAD: Pakistan's air force on Monday scrambled fighter jets over several major cities in a sign of increased 'vigilance,' following last month's deadly attacks on Mumbai.

'In the current environment, PAF has enhanced its vigilance,' chief air force spokesman Air Commodore Humaun Viqar Zephyr told AFP.

Residents in the capital Islamabad, the nearby garrison city of Rawalpindi and the eastern city of Lahore made panicked telephone calls to media outlets to ask about the low-flying fighter jets.

Two civilian flights were delayed due to the air force's exercise, an airline official said.

'Two of our flights were delayed for some time because the PAF was conducting some exercises but now everything is back on normal,' said Muhammad Latif, a spokesman for Pakistan International Airlines, referring to the air force (PAF).

The flights were delayed at the airport in Lahore, near the Indian border, Latif said, while dismissing television news channel reports of a high alert at Pakistani airports.

Pakistan last week summoned a senior Indian diplomat in Islamabad to protest against recent alleged airspace violations by Indian warplanes.

Indian fighter jets had crossed into Pakistani airspace over Kashmir and Punjab province, the government said on Dec 13.

Pakistan said its own fighter jets were scrambled to chase off the intruders, but it also played down the incident by describing the violations as 'technical' and 'inadvertent.'

India denied any violation of Pakistani airspace.