US and Afghan troops were pressing an assault against Al-Qaeda and Taliban positions in the Tora Bora mountains of eastern Afghanistan, the last known hiding place of Osama bin Laden.
The US military announced the air and ground attack on militant positions in the mountain range near the Pakistani border yesterday, but they did not say how long the offensive would last.
The operation was launched against carefully targeted militant positions, US military spokeswoman Captain Vanessa Bowman told AFP.
"US and Afghan forces engaged Al-Qaeda and other violent extremist fighters in eastern Afghanistan during a combined arms assault using precision munitions," Bowman added in a statement.
Fugitive Al-Qaeda leader bin Laden was last seen in the Tora Bora mountains in December 2001 when the US launched a failed operation with Afghan allies to prevent him fleeing the country in the aftermath of the 9-11 attacks.
It is widely believed that bin Laden escaped from Tora Bora into the northern tribal areas of Pakistan where intelligence agencies believe he is currently hiding.
The area, a complex of caves some 50 kilometres south of the eastern city of Jalalabad, is known as the last stronghold of Al-Qaeda in Afghanistan.
Bin Laden and fighters from Arab countries built the complex network of caves at Tora Bora in the 1980s during the resistance to the Soviet occupation of Afghanistan.
US spokeswoman Bowman said the mountainous and remote region was an ideal environment to conceal militant support bases and training sites, as well as plan attacks.