With Al-Qaeda [Images] leader Osama bin Laden's trail having gone cold, the Bush administration is expected to double the sum on his head to $50 million by the end of February and chalk out a publicity blitz to help trace him.

As part of the publicity blitz, the US state department is reminding Afghans and Pakistanis of the existing $25 million bounty, according to Time magazine.

Bin Laden is still thought to be hiding somewhere along the 2,500-km mountainous Afghanistan-Pakistan border, but intelligence officials in Kabul and Islamabad believe there has been no trace of him for the past 20 months.

State department advertisements began appearing this month in Jang, a widely circulated Pakistani newspaper, offering rewards for bin Laden, his lieutenant Ayman al-Zawahiri, Taliban leader Mullah Mohammed Omar and 11 others.

The advertisements have elicited an average of 12 responses a day and will be followed by an advertising barrage on regional radio and TV stations in the borderlands and cities where the Al-Qaeda chief may be hiding, Time quoted the state department as saying.

US reward offers were posted soon after terrorist attacks on New York and Washington, DC, but Time said officials concede that little effort was made to circulate the offers widely in the Afghan and Pakistani countryside.

Even if a local knew of bin Laden's whereabouts, the informer would face daunting obstacles in contacting US authorities, the report said.

Congressman Mark Kirk, the Republican who wrote the bill boosting the reward and who just travelled to Pakistan, said it is possible bin Laden is not in some snowy mountain cave but has melted away into one of the teeming Pakistani cities.

"What we're looking for is some young Pashtun living in a town who knows the value of $25 million and can figure out how to reach us safely," said Kirk.