Taliban-led forces fighting US and Nato troops in Afghanistan have increased nearly fourfold since 2006, according to a US intelligence estimate presented to the US president.
The report says that the number of Taliban fighters has grown to 25,000, from 7,000 four years ago, the officials said on Friday as Barack Obama convened a fifth cabinet-level meeting on his country's military strategy in Afghanistan.
The US president is considering whether to agree to a request by the senior commander of US and Nato forces in Afghanistan for up to 40,000 extra troops to be deployed.
General Stanley McChrystal has warned that the US mission in Afghanistan risks failure unless more troops are sent to combat the Taliban and provide training and support to Afghan government forces.
Officials said on Friday that Obama - who agreed early in his presidency to send 21,000 extra troops to Afghanistan - has not made any firm decision in regard to McChrystal's request.