The ambassador was en route to the Pakistani embassy in Kabul

The technicians went missing on the same day as Pakistan's ambassador to Afghanistan, Tariq Azizuddin, was reportedly abducted in the same region.

Mr Azizuddin had been going overland from the city of Peshawar to Kabul.

Pakistan's north-west has witnessed fierce fighting between Islamist militants and government troops.

The pro-Taleban guerrillas declared a unilateral ceasefire last week after months of clashes with troops garrisoned there.

The workers from Pakistan's Atomic Energy Commission were on a mission to map mineral deposits in the mountains when they were kidnapped, police say.

"The technicians were going for some geological survey in the area when they were kidnapped at gunpoint along with their driver," Romail Akram, a senior police official, told Reuters news agency.

Their vehicle was intercepted by masked gunmen in the Dera Ismail Khan district, a stronghold of local militants.

"We don't know if the abductors were militants or members of some criminal gang," a local police chief, Akbar Nasir, told the AFP news agency.

He said efforts to locate the missing men had yet to yield any results.

Karzai concerned

Efforts are also continuing to locate the missing Pakistani envoy, Tariq Azizuddin.

Mr Azizuddin went missing on Monday as he was travelling overland from the Pakistani city of Peshawar to the Afghan capital, Kabul.

Afghan President Hamid Karzai said he was certain the envoy had been abducted, adding: "I hope he is safe and I hope he will be released soon."

The Khyber region has long been a base for bandits and smugglers but has seen little of the unrest linked to an uprising by Islamist militants in adjoining areas.

Pro-Taleban militants recently kidnapped more than 200 Pakistani troops in the South Waziristan region.

The soldiers were reportedly released in a prisoner exchange with Pakistani authorities.

'Protected road'

Pakistan's government has refused to confirm Mr Azizuddin has been kidnapped, saying only that he was missing.

The Pakistani embassy in Kabul said contact was lost with Mr Azizuddin at around 1045 local time (0645 GMT) on Monday.

The rugged region near the Afghan border has seen heavy fighting

There were reports on Pakistani television of his car going through a checkpoint without stopping.

An official of the Khyber agency tribal administration told the BBC that the ambassador went through the Khyber agency without taking a security escort that was waiting for him at the start of the tribal territory.

Correspondents say that such escorts are routinely sent with dignitaries and officials when they travel through tribal areas.

But some travellers dispense with them because they think it makes their movements more noticeable.

Mr Azizuddin is said to have previously travelled to Kabul by road, often without the tribal security escort.

The route through the agency is believed to be the shortest and quickest way between Peshawar and Kabul.

Being the main trade route, the Khyber agency road is busy in daylight hours, supplying reinforcements and to the US and Nato forces in Afghanistan.

It is also one of the most protected of all the tribal roads, with a contingent of tribal police posted every 100m. The paramilitary Frontier Corps have a fort along the road.