General Dan McNeill said the International Security Assistance Force (ISAF) had scored tactical successes against Taliban rebels in the last year, but more needed to be done to bring security, development and good governance to Afghanistan.
Weapons from neighboring countries only exacerbated the problems of achieving those goals, the U.S. general added.
ISAF, McNeill said, "intercepted a weapons convoy on September 5 in the western part of this country. This weapons convoy clearly geographically originated from Iran. This convoy contained a number of advanced technology improvised explosive devices.
"It is difficult for me to conceive that this convoy could have originated in Iran and come to Afghanistan without at least the knowledge of the Iranian military," McNeill told a news conference.