Kabul: US and Afghan air and ground forces pounded Al Qaida militants for a second day on Thursday in the Tora Bora mountains close to the Pakistan border where Osama Bin Laden once fled in the wake of the 2001 invasion.
The steep slopes of the mountains are riddled with cave and tunnel complexes built by Afghan and Arab fighters during the 1980s struggle against the Soviet occupation and provide an ideal hideout for guerrilla fighters.
"It is a joint operation conducted by Afghan and US forces, divided by ground and air assets," said Captain Vaness Bowman, spokeswoman for US-led coalition forces in Afghanistan.
"Afghan and US forces engaged Al Qaida and other violent extremist fighters in the eastern Afghanistan region in Tora Bora," she said, adding that the operation began on Wednesday.
"I personally don't have any casualty reports at this time, but we do know that there have been substantial casualties."
Three coalition soldiers were killed in a roadside bomb in the Khogiani district near Tora Bora on Sunday and a US base in the area also came under rocket attack in the last few days.
US soldiers and Afghan militia forces launched a major assault on Tora Bora in late 2001 in pursuit of Al Qaida and its leader, Osama Bin Laden, who was thought to be hiding in the mountain range after the toppling of the Taliban government.
But US military leaders allowed the Afghan militiamen to spearhead the assault and Bin Laden managed to escape.
Al Qaida forces and their Taliban allies use the rugged and semi-lawless border region between Afghanistan and Pakistan to plan, train and launch attacks in both countries.