Gates, who on Tuesday confirmed that an extra 3,200 US marines were being sent to the war-torn country, praised the work of Nato troops in Afghanistan's southern provinces.
"Allied forces from the United Kingdom, Canada, the Netherlands, Australia and Denmark and other nations have stepped up to the plate and are playing a significant and powerful role in Afghanistan," he said.
"They have rolled back the Taliban from previous strongholds in the south.
"They are taking the fight to the enemy in some of the most gruelling conditions imaginable."
Nato allies had responded to the Los Angeles Times interview with concern.
Britain insisted its troops had extensive counterinsurgency training, while the Netherlands summoned its US ambassador for an explanation.
Gates phoned his Canadian counterpart to say his quotes had been taken out of context.
His Thursday briefing, originally expected in the afternoon, was also rescheduled to meet European news media deadlines.
Gates, however, reiterated his view that Nato forces had inadequate training for counterinsurgency operations in an alliance set up to confront the Soviet Union.
"We have to acknowledge that the alliance as a whole has not trained for counterinsurgency operations even though individual countries have considerable expertise at and success in this arena," he said.
The US has struggled for months to convince other states to send more troops to Afghanistan.
Gates told US National Public Radio on Thursday that he had reluctantly asked George Bush, the US president, to approve the additional troops because it was clear European nations would not send more troops to Afghanistan.
The US marine reinforcement will increase the US troop presence by about 10 per cent, from 27,000 to about 30,000.