The news comes amid increasing violence in Afghanistan, including two attacks in as many days against NATO forces in the country's capital, Kabul.
The Chicago Tribune first reported that a major offensive is planned that would involve thousands of American troops and include going after refuges in Pakistan used by al-Qaida, according to military sources.
"When the winter snows thaw in Afghanistan, the Taliban and al-Qaida come out (of hiding)," an unnamed official said. "It's just prudent to have our forces ready to go after them."
Another U.S. official told Reuters the offensive would be similar to past operations in which U.S. Special Operations and other troops went after guerillas and transit routes in the mountains near the Afghanistan-Pakistan border.
But the Pakistani government denied that it would allow such an operation to extend into its territory, according to Reuters. Pakistani President Gen. Pervez Musharraf said at a news conference last week that he would not consider allowing U.S. troops to join in the search for fugitive al-Qaida leader Osama bin Laden on Pakistan's side of the border.
"It's a very sensitive issue. There is no room for any foreign elements coming and assisting us, we don't need any assistance," Musharraf said.
Musharraf, who is cooperating with Washington against al-Qaida but is under pressure from Islamic parties at home, has allowed only limited U.S. military presence in his country.
CNN reported that a senior Defense Department official said troops, supplies and logistics have been ordered to carry out the operation, which is designed to prevent al-Qaida forces from regrouping during the warm weather.
About 8,500 Americans are among the 11,500 international troops that remain in Afghanistan. About 5,000 other troops under NATO command are serving as peacekeepers in Kabul.
Lately, the Taliban has said it would target coalition forces until they leave the country.
On Wednesday, a suicide bomber drove a taxi carrying explosives up to a vehicle carrying British soldiers who were part of a NATO-led force. The blast killed one of the soldiers and wounded three others.
The explosion occurred on the road leading east out of Kabul to Jalalabad, near where four German peacekeepers were killed and dozens injured in June also by a suicide bomber driving a taxi, Reuters reported.
On Tuesday, a bomber threw himself in front of a vehicle carrying Canadian troops as it slowed to navigate a speed bump on the outskirts of Kabul. One Canadian soldier and an Afghan civilian died.
Members of the Taliban claimed responsibility for the Tuesday and Wednesday attacks.