Kerry said three conditions -- sufficient Afghan troops, reliable local assistance and sufficient development aid -- must be met before additional troops could be deployed to the country, The Hill reported.
"I am convinced from my conversations with Gen. Stanley McChrystal that he understands the necessity of conducting a smart counterinsurgency in a limited geographic area," Kerry said in a speech at the Council on Foreign Relations. "But I believe his current plan reaches too far, too fast."
Kerry, the chairman of the Senate Foreign Relations Committee, said he may eventually support a troop surge despite his concerns.
"Under the right circumstances, if we can be confident that military efforts can be sustained and built upon, then I would support the president should he decide to send some additional troops to regain the initiative," Kerry said.
Kerry also ripped former Vice President Dick Cheney for accusing President Barack Obama of "dithering" on the troop decisions. Cheney said Obama's lack of a decision so far was endangering troops.
"After eight years of neglecting Afghanistan as vice president, Dick Cheney has now come out of retirement to criticize President Obama for taking time to examine assumptions before sending troops into war," Kerry said.