Four heavily-armed terrorists, travelling in a truck to Kashmir after infiltrating from Pakistan, were killed in a "chance encounter" with security forces here early Wednesday morning, a police officer said, terming it as a "major success" ahead of Republic Day.

Additional Director General of Police, Jammu zone, Mukesh Singh said the gunfight took place around 7.30 am amid intense fog near Tawi Bridge in the Sidhra bypass area along the Jammu-Srinagar national highway.

Singh, who was flanked by General Officer Commanding of Army's Tiger division Maj Gen Gaurav Gautam, told reporters at the scene that bodies of four terrorists have been recovered from the truck.

The truck which was carrying the four heavily armed terrorists had a fake registration plate and tampered engine and chassis numbers, Mukesh Singh said.

"Seven AK assault rifles, one M4 rifle, three pistols and a large quantity of ammunition were recovered from the slain terrorists," he said.

"A suspicious movement of a truck, that was moving towards Kashmir, was observed. It was followed and stopped near Sidhra check point, but its driver escaped on the pretext of attending the call of nature," the ADGP said.

Getting suspicious, Singh said, police started searching the truck but came under heavy fire from inside.

An encounter ensued during which the truck caught fire, he said, adding the terrorists were killed.

The ADGP said the ultras were heavily armed and were on their way to Kashmir when they were intercepted.

He said efforts are on to nab the driver of the truck, who has fled.

"The identity and group affiliation of the terrorists is awaited," the ADGP said.

Earlier, talking to PTI, Director General of Police (DGP) Dilbag Singh said so far three terrorists have been killed. "The number could be more," he added.

Asked whether the terrorists came from across the border and were picked by the truck driver to ferry them to Kashmir, he said it is matter of investigation.

Officials said the intense firing between the two sides lasted for over 45 minutes, during which several explosions apparently caused by hurling of grenades, were heard.

Smoke was seen blowing from the truck, loaded with husk, and was completely damaged in the gunfight.