About 1,000 US troops raided on villages in southeastern Afghanistan overnight in a hunt for al-Qaeda members.
Helicopters ferried troops from the Army's 82nd Airborne Division to the remote, mountainous area as the hunt for Osama bin Laden intensified, according to US military officials in Washington.
The troops left from their base in Kandahar, the former Taliban stronghold in southern Afghanistan.
Radio transmissions had been detected coming from caves above the villages, military officials said.
It was the largest US military operation in Afghanistan since Operation Anaconda just over a year ago. That eight-day battle involved hundreds of Taliban and al-Qaeda fighters against thousands of US and allied Afghan troops.
There have been a series of raids on both sides of the Afghanistan-Pakistan border in the weeks since authorities captured al-Qaeda's Number three figure, Khalid Sheikh Mohammed, in Pakistan on March 1st.
Authorities have said Mohammed is giving information to US interrogators and have said some of the subsequent arrests came as a result of Mohammed's capture.