QUETTA (Pakistan) - PAKISTAN on Tuesday detained several suspects over the kidnapping of a top American UN official in restive Baluchistan province amid an 'all-out' effort to track him down.

John Solecki, head of the UN refugee agency (UNHCR) in the southwestern city of Quetta, was abducted at gunpoint on Monday while travelling to work. His driver was killed.

It is the highest-profile Western abduction in Pakistan since US journalist Daniel Pearl was kidnapped in January 2002 and beheaded by Al-Qaeda militants, and underscores the difficulties the country faces in containing violence.

Pakistani officials admitted Tuesday they had no clue who snatched Solecki and where he had been taken, given the myriad of criminal gangs, insurgent rebels and Islamist militants known to operate in Baluchistan, which borders Afghanistan.

'We have picked up several suspects in connection with the probe. These people are detained for questioning, although we still have no direct lead on the kidnapped official,' a senior security official told AFP.

'So far there has been no claim of responsibility. We have intensified police patrolling. Security has been intensified along the Afghan border to ensure the official has not slipped through the border into Afghanistan.'

Quetta, which has an estimated population of just under one million, is considered a possible refuge for Taliban leaders who fled Afghanistan after the US-led invasion in late 2001 that toppled the hardline regime.

'It is still not clear whether the kidnapping is the work of a criminal gang or Taliban insurgents,' added the security official, who is involved in the investigation but requested anonymity because he was not authorised to speak.

'We are making an all-out effort to track down the official,' he said.

Mr Solecki's white jeep marked with UN insignia hit a brick wall during the ambush and a small pool of blood was seen on the pavement next to the driver's door, an AFP photographer witnessed.

Pakistan denounced Monday's attack as an 'dastardly terrorist act.' In the capital Islamabad, the interior ministry said provincial governments nationwide had been ordered to step up security for UN staff.

'The provincial governments have been asked to upgrade and reinforce the security of all UN employees throughout the country,' Kamal Shah, the most senior official at the ministry, told AFP.

'The authorities have mobilised police, intelligence and security personnel to hunt down the kidnappers and to recover the UN official safely,' he said.

The authorities in Baluchistan were told 'Mr Solecki must be recovered,' Mr Shah added.

Pakistani police and diplomats have confirmed Mr Solecki is American, but the US embassy in Islamabad has been tight-lipped.

'We are aware of the media reports. We are working with the Pakistani and United Nations' authorities to gain more information,' embassy spokesman Lou Fintor told AFP.

The ambush came two days before UN chief Ban Ki-moon was expected to visit.

Mr Ban, who has been attending a summit of the African Union in Addis Ababa, called for Solecki's 'immediate and safe release,' UN deputy spokeswoman Marie Okabe told a press briefing at UN headquarters in New York.

Baluchistan province has rich energy resources but is rife with regional insurgency, sectarian violence and attacks blamed on Islamist extremists, making it difficult to pinpoint quickly who was behind the assault.

Hundreds of people have died in insurgent unrest in the province since 2004, when rebels began demanding political autonomy and a greater share of profits from Baluchistan's natural resources.

Kidnappings of foreigners in Baluchistan are rare, although they have multiplied in northwest Pakistan, which also borders Afghanistan. -- AFP