"The combined effort of allied forces with the Afghan government is the way we will defeat the insurgency, the way we will stop al-Qaeda having any space to operate in Afghanistan," Brown said.
Brown said the supplies are part of a plan to weaken the Taliban and to strengthen the Afghan authorities.
But he said the next few months would be "obviously critical", and would depend on the new Afghan government headed by Karzai.
"We have good cooperation and we're hoping, with the new [Afghan] Cabinet, to work on fighting corruption and take a step toward improving security in Afghanistan."
Karzai, who is under Western pressure to crack down on corruption after being re-elected in a poll marred by fraud, vowed to do more to create an accountable Cabinet.
He said he is working to assemble a group of Cabinet ministers, which he will announce in coming days.
"We need to have a government that is responsive to the needs of the Afghan people," he said.
"That's our responsibility and we will be taking a lot more measures."
Brown, who has been critical of corruption in the Afghan government, welcomed Karzai's remarks.
"Of course, people will judge what happens by results, but I think we have seen a determination on the part of President Karzai to take new action against corruption," he said.