Al-Qaeda's leader in Afghanistan is preparing to relaunch his war-shattered organisation when international forces withdraw from the country if no security agreement is reached.
Farouq al-Qahtani al-Qatari had been bringing in experienced militants to train a new generation of fighters, US officials said.
They said the US had stepped up drone and jet missile strikes against Qahtani and his followers in the mountainous eastern provinces of Kunar and Nuristan.
The objective war to keep him from restarting the large training camps that once drew hundreds of followers before the US-led war began.
The officials say the counterterrorism campaign - a key reason the Obama administration agreed to keep any troops in Afghanistan after this year - could be jeopardised by the possibility of a total pullout.
House Intelligence Committee Chairman Mike Rogers said the number of al-Qaeda members in Afghanistan had risen, but potential recruits were "waiting for the US to fully pull out".
The administration was set to leave 10,000 troops in Afghanistan after combat operations end on December 31, to continue training Afghan forces and conduct counterterrorism missions.
But without a security agreement authorising international forces to stay in Afghanistan, Barack Obama has threatened to pull out all troops.
After talking to Afghan President Hamid Karzai last week, Obama ordered the Pentagon to begin planning for the so-called zero option. US officials say unless they can continue to fly drones and jets from at least one air base, Qahtani could plan new attacks against US targets.