A suicide bomber blew up his explosives-filled car on a Pakistani motorway early on Sunday, killing a patrol officer, the chief of motorway police said.
The attack took place near Lillah, about 140 kilometres (87 miles) south of the capital Islamabad, on a motorway which links several main cities and towns in Pakistan.
"A suicide bomber blew up his car, when he was intercepted near an interchange," inspector general of the national highway and motorway police Waseem Kausar told AFP.
A patrol officer, who intercepted the car to check on its occupants because of prior intelligence information, was killed when the suicide bomber triggered the explosives, Kausar said.
Another man travelling with the suicide bomber tried to run away when the car was stopped but was later arrested by police, he said.
During an initial investigation the arrested man said the two men were on their way from the city of Peshawar, the capital of restive North West Frontier Province, to Lahore, Kausar said.
But another senior police official later said that it was still not clear if there had been a second man in the car because the investigators had not yet found the remains of the man believed to be the suicide bomber.
"So far the body parts of the other man have not been found. Investigations are continuing and according to initial investigation only one man has been arrested," regional police chief Aslam Tarin told private Express television.
Tarin said that according to initial information the detained man was driving the car.
The official said that some 30 kilograms (66 pounds) of explosives were used in the bombing.
Kausar said that the blast was so strong it was heard in a radius of 15 kilometres (nine miles).
A series of attacks blamed on extremists has left nearly 200 dead this month in Pakistan, the frontline state in the US-led battle against global Islamist extremism.
On October 10, militants ambushed the army headquarters in Rawalpindi in an audacious raid claimed by the Tehreek-e-Taliban in Pakistan (TTP) movement.
Prime Minister Yousuf Raza Gilani has condemned the recent violence and vowed the government would not waver in its resolve to "root out terrorism", with nearly 30,000 troops fighting against the TTP in South Waziristan.
The offensive presents the nuclear-armed country with its toughest fight to date against the radicals, blamed for attacks that have killed 2,280 people in Pakistan in two years.