General Ray Henault, the Canadian general who chaired talks among national defence chiefs in Warsaw, told a news conference on Saturday:"Our collective assessment is that we are satisfied with military-related progress to date, particularly in the north and in the west, but less so in the south."

No pledges of extra troops were announced after two days of talks but Nato officials said the defence chiefs had agreed to consult with their capitals on reinforcements to tackle fiercer-than-expected Taliban resistance.

Asked whether the defence chiefs had indicated that they would come up with 2,000-2,500 troops, which Nato planners say they want for an offensive against Taliban insurgents in the south, he said:

"I can't give you the exact number; but the chiefs of defence are very aware of requirements...Raising the number of troops will be a political decision."

Henault said they also agreed to review the caveats, or restrictions imposed by individual Nato nations on what their troops could do, ranging from a ban on night-flying to deployments in direct combat in the violent south.

"In our meeting, we discussed national caveats and pressed for the need to reduce them to the minimum possible," he said.

Nato casualties

"I can't give you the exact number; but the chiefs of defence are very aware of requirements...Raising the number of troops will be a political decision"

General Ray Henault, the Canadian general who chaired the meeeting

Nato says it has killed more than 300 insurgents and cornered hundreds more in the south since it launched its biggest offensive against the Taliban a week ago. The Taliban denies the figures.

British, Dutch and Canadian troops leading the mission in the south are taking almost daily casualties in what is the toughest ground combat mission in Nato's 57-year history.

Under pressure from Washington to do more, Nato expanded its operations from the north, west and Kabul to the south a month ago despite nations having only come up with about 85 per cent of military requests for troops and equipment.

But alliance leaders acknowledged on Thursday that they had underestimated the strength of Taliban opposition and called on countries to fill remaining commitments amounting to 2,000 to 2,500 troops plus helicopters and transport aircraft.

Germany, which leads Nato operations in the relatively quiet north, is seen under pressure to make reinforcements available despite vocal political opposition in Berlin to such a move.

Nato commanders until recently insisted that caveats, long a bane of other Nato operations, were not an issue in Afghanistan.

But the rising violence in Afghanistan appears to have prompted them to call for greater flexibility in how they can use troops.