NATO forces will fight through the bitter Afghan winter to step up the pressure on the Taliban, concentrating on their strongholds in the south and east, a spokesman for the alliance said Monday.

"The Taliban will be under pressure over the next three months' winter time," Brigadier General Josef Blotz told a news conference in Kabul.

"We're making progress and now it is about holding on this progress," he said. "This progress is not irreversible yet."

NATO-led forces are battling Taliban militants in their strongholds in the southern provinces of Kandahar and Helmand.

"We'll put the pressure everywhere, in Kandahar, in Helmand, in Region Combat East, everywhere," the German general said.

The bitter Afghan winter traditionally marks a pause or at least a decrease in fighting, due to the frigid temperatures and heavy snowfall but also because militant fighters head to more temperate climes, notably in neighbouring Pakistan.

"We've got the resources right now in terms of force, not only to clear areas (in Kandahar and Helmand) but also to hold," said Blotz in response to a question about districts which have become unstable again after NATO had said they were secure.

The spokesman welcomed the increase in the Afghan police and army which he said currently numbered 263,000 in total.

Afghan forces are due to assume responsibility for security from foreign troops forces by 2014 under an agreement between NATO, the United States and the Afghan government reached last month at a NATO summit in Lisbon.