Nato's leaders have urged member countries to provide reinforcements to help in its campaign against Taleban guerrillas in southern Afghanistan.
Secretary General Jaap de Hoop Scheffer criticised some member states for, in his view, not doing enough.
The commander of British forces in Afghanistan has meanwhile said combat there is more intense than in Iraq.
Brigadier Ed Butler said his troops were being attacked up to a dozen times a day but their morale remained high.
"The intensity and ferocity of the fighting is far greater than in Iraq on a daily basis," Brig Butler told the UK's ITV News programme.
He said British forces had been involved in "fighting that is up close and personal" that at times included hand-to-hand combat.
Earlier, Nato's top commander, Gen James Jones, said the alliance had been taken aback by the scale of violence in the region.
But he predicted that the coming weeks would be decisive in the fight against the insurgents.
Commanders on the ground had asked for several hundred additional troops and more helicopters and airlift, he said.
"We are talking about modest reinforcements," he told reporters at Nato European headquarters in Belgium.
His comments were echoed by Mr de Hoop Scheffer.
"Those allies who perhaps are doing less in Afghanistan should think: 'Shouldn't we do more?' There are certainly a number of allies who can do more," he told reporters in Brussels.
About 20 foreign soldiers, most of them British or Canadian, have been killed in fierce fighting with Taleban guerrillas since the alliance extended its peacekeeping mission in the south a month ago.
Nato troops took over leadership of military operations in the region from the US in July.
Gen Jones is due to meet generals from the 26 Nato nations this weekend in Warsaw, Poland.
The US marine general said he would initially ask for reinforcements from existing contributors to the 37-nation International Security Assistance Force (Isaf), including Germany, which has several thousand troops in the calmer north of the country.
Gen Jones told reporters that Nato forces had expected some opposition in southern Afghanistan, but added: "We should recognise we are a little bit surprised at the level of intensity, and that the opposition in some areas are not relying on traditional hit-and-run tactics."
However, he said he was confident the situation could be contained relatively quickly.
He said reinforcements "will help us reduce casualties and help us bring this to a successful conclusion in a shorter period of time".
BBC diplomatic correspondent Jonathan Marcus says the general's comments are a blunt recognition that Nato commanders do not have the resources they need.
Many analysts believe there were serious shortcomings in the intelligence assessments that established the initial mission, and that harder fighting was to be expected.
What is urgently needed, our correspondent says, is a battle group of several hundred men with reconnaissance and support elements which would give commanders the flexibility they say they need.
But even if this reinforcement is forthcoming, many analysts are still sceptical that Nato can achieve its wider goals in Afghanistan, our correspondent adds.
The Taleban ruled Afghanistan until late 2001 when they were toppled by US-led forces in the wake of the 11 September attacks on New York and Washington.
Pakistani President Pervez Musharraf on Thursday acknowledged that al-Qaeda and Taleban militants continue to cross from Pakistan into Afghanistan to launch attacks.
But the president, wrapping up a two-day visit to Afghanistan, denied allegations that Pakistan's powerful military Inter-Services Intelligence (ISI) was helping them.
"Let me say neither the government of Pakistan nor the ISI is involved in any kind of interference inside Afghanistan," he told Afghan government and army officials.