Pakistan President Pervez Musharraf's plane was fired on as it took off on Friday from a military airfield in Rawalpindi, an Intelligence officer said, contradicting official denials.
Musharraf's plane arrived safely in the southwestern town of Turbat, where the president visited flood victims, and the military denied there had been any attack.
But an Intelligence official, speaking on condition of anonymity, said there had been an unsuccessful attempt on Musharraf's life.
Previous bids on Musharraf's life
Dec 14, 2003: survived an assassination bid when a powerful bomb went off minutes after his highly-guarded convoy crossed a bridge in Rawalpindi.
Dec 25, 2003: two suicide bombers tried to kill Musharraf, but their car bombs failed to kill the president; 16 others nearby died instead.
A Reuters photographer saw two large guns mounted on the roof of a two-storey house in the congested area close to the airport, and a neighbour said he heard the firing.
One appeared to be a long barreled anti-aircraft gun and the other a light machine gun.
They were placed between large satellite dishes and a water tank of the flat-roofed house, located directly under the flight path close to the runway. A low wall ran round the perimeter of the roof.
Security is normally deployed in the area ahead of president's flights. The timings of Musharraf's flights are generally kept secret.
Neighbour Arshad Mehmood said the house had been vacant and up for rent, though a couple with two children had visited it the previous night.
Security forces have cordoned off the area around the house in the garrison town next to the capital, Islamabad, and the owner, a shopkeeper, had been detained.
US ally Musharraf survived two assassination attempts by Al-Qaeda-linked militants in Rawalpindi in December 2003.
According to some accounts given by television reporters a rocket was also fired at the plane.
But the Pakistan military was adamant there had been no attack.
"There was no firing at the president's plane. He is in Turbat," an army spokesman said.
Musharraf has been a hated figure among Pakistani militant groups since he abandoned support for the Taliban and sought peace with India over the disputed territory of Kashmir.
The reports of a fresh assassination attempt came as Pakistani security forces laid siege to a mosque in Islamabad where a radical cleric and hundreds of followers were holed up after clashes on Tuesday.
At least 19 people have been killed so far in the clashes and bloody stand-off.