Gen. Stanley McChrystal included an option to send at least 60,000 more US troops to Afghanistan.
Obama faces pressure to choose an Afghanistan plan that doesn't call for huge commitment of troops.
Some tribes have forced insurgents from their area, but many risks remain.
As officials consider sending more troops to Afghanistan, some worry about the lack of a larger plan.
Tehrik-e-Taliban carried out Sunday's bombing, the deadliest since the new Pakistani government took power in March. The suicide attack came two days after the militants freed the Pakistani ambassador to Afghanistan, Tariq Azizuddin.
Pentagon weighs lead role in NATO's combat mission in the south to better fight Taliban.
The focus of the 24th Marine Expeditionary Unit is largely security, but will include humanitarian work.