"We don't have progress as evenly or as fast as many of us would like, but we are not losing Afghanistan," he said.
His comments came as up to 100 Taliban fighters were reportedly killed in two separate battles with international coalition forces in southern Afghanistan, officials said.
The Nato-led International Security Assistance Force (Isaf) said fierce fighting erupted after Taliban fighters attacked an Afghan security force base on the outskirts of the town of Lashkar Gah, the capital of Helmand province.
Isaf said the attack took place on Saturday.
According to Afghan authorities, the fighting started at around midnight and lasted for approximately three hours.
Al Jazeera's Dan Nolan, reporting from Kabul, said that an Afghan official based in Lashkar Gah described the attack as the "worst fighting he's ever seen in the town".
Captain Mark Windsor, an Isaf spokesperson, told Al Jazeera that the military "does not do body counts".
"We do not try to figure out the number of insurgents killed ... once you get into the details or try to guess a number, then things might be different to what you said at the beginning," he said.
"What we do know is that this was a planned attack against the Afghan base, where they had tried to take over the compound. What followed was an operation to battle these insurgents."
Daud Ahmadi, a spokesman for the Helmand government, said 64 Taliban fighters were killed.
But that could not be independently verified and journalists are not able to travel to the remote and dangerous battle sites.
In a second battle, in Helmand, Afghan and international troops retook the Nad Ali district centre - which had been held by fighters - during a three-day fight, Ahmadi said.
That battle, which also involved air strikes, ended on Saturday and resulted in the death of 40 Taliban fighters, officials said.
Afghan police and soldiers were now in control of the district centre.
Nato said its aircraft bombed fighters after they were seen gathering for a major attack, killing "multiple enemy forces".
"If the fighters planned a spectacular attack prior to the winter, this was a spectacular failure," Richard Blanchette, an Isaf spokesman, said.
Helmand is the largest drug-producing area in the world, and the region alone accounts for more than half of Afghanistan's production of opium poppies.
More than 90 per cent of the world's opium is produced in Afghanistan, and up to $100m of the trade's profits are used to finance the Taliban.
The violence has killed more than 4,700 people this year, according to an Associated Press tally of figures from Western and Afghan officials.