|Bin Laden was sheltered by the Afghan Taliban before the September 11 attacks [GALLO/GETTY]
Twenty-five foreign fighters were killed and wounded by Afghan security forces after they crossed the border from Pakistan, a government official told the Reuters news agency.
Jamaluddin Badr, governor of northeastern Nuristan province, said on Tuesday that the operation was launched to guard against attacks after al-Qaeda leader Osama bin Laden was killed a day earlier.
"As a result of the operation, 25 foreign fighters were killed and wounded," Badr said. Those killed included Arabs, Chechens and Pakistanis, he said.
The operation was in the Barg-e-Matal district of Nuristan, very close to the border with Pakistan, Badr said.
The incident was the first sign of possible retaliation in Afghanistan since bin Laden's death.
"We are aware of the situation here now that al-Qaeda and other elements will try to infiltrate into Afghanistan. We have launched an operation to control border infiltration," Badr said.
Bin Laden - the alleged architect of the September 11, 2001, attacks on the United States - was killed by US forces in a dramatic raid north of the Pakistani capital, Islamabad, on Monday, sparking fears of retaliatory attacks by Islamist fighters.
Fears of retaliation
Taliban, al-Qaeda and other armed groups have long operated out of safe havens and training camps in Pakistan's largely lawless northwest Pashtun tribal regions.
Bin Laden was sheltered by the Afghan Taliban before the September 11 attacks and managed to escape US troops and Afghan militia during an assault in Afghanistan's mountainous Tora Bora region before slipping across the border into Pakistan.
Military and political leaders and analysts have warned that the immediate short-term effect of bin Laden's killing for Afghanistan would likely be a spike in violence as fighters seek to strike back.
Even before bin Laden's killing, senior NATO commanders warned a big wave of violence was expected this week and the Afghan Taliban announced at the weekend it would begin a new wave of violence as part of the spring fighting season.
Fighting traditionally picks up in Afghanistan when winter snow melts allowing fighters to move through the mountains.