The defence secretary, Des Browne, will admit today that Britain and its Nato allies seriously underestimated the strength of the Taliban and the violent resistance faced by western forces in Afghanistan. "The Taliban's tenacity in the face of massive losses has been a surprise, absorbing more of our effort than predicted and consequently slowing progress on reconstruction," he will say in a speech to the Royal United Services Institute in London.

Though he says it was expected that the Taliban would fight hard, he will add: "We do have to accept that it's been even harder than we expected."

The defence secretary is also expected to tell his audience: "Success won't be what we understand by security and prosperity and proper governance, but it will be progress and it will be massively worth achieving." He is expected to admit that that seemed "some way off" against the current background of intense fighting and of little progress on building up public institutions and infrastructure in southern Afghanistan.

The speech comes amid a wave of violence in Afghanistan and concern over the scale and nature of the mission. Nineteen British soldiers have been killed in southern Afghanistan this month.

Yesterday there further signs of escalating bloodshed with three separate suicide attacks. In Kandahar, four Canadian troops were killed and at least 27 other civilians wounded, most of them children, according to Afghan police who said the troops were handing out notebooks and pens to children.

Another suicide attacker blew up his bomb-packed car in the Afghan capital, Kabul, killing four policemen. In the normally peaceful city of Herat, 11 people were killed, the province's governor said. The blast was caused by a suicide bomber on a motorcycle; the province's deputy police chief was among 18 wounded.

With the US and the UK seeking to bolster the Afghan mission, Mr Browne is expected to reflect concerns expressed by military chiefs by reminding Britain's Nato partners of their commitments to send more troops to southern Afghanistan. The message is that they, too, must realise that Afghanistan had to be "a success", a defence official said last night.

Mr Browne will recognise that British troops are operating in "arduous conditions, around the clock". He will insist they are fighting in a "noble cause" and that it is in Britain's interest, as well as that of the Afghan people, that they succeed.

British troops were "fighting and working in these conditions because this is the nature of conflict - hard, dirty and beyond the experience of most of us to understand", Mr Browne is expected to say.

He is also likely to point to what has been achieved in the west and north of the country - "more and better schools, new jobs and the return of millions of refugees". In a move highlighting the growing pressure on British troops, Mr Browne yesterday agreed to send an extra RAF Harrier fighter-bomber to support soldiers on the ground. It will join the six Harriers already based at Kandahar air base. He said the move was in response to a "surge" in demand for close air support from British and other international troops fighting the Taliban.

Yesterday's violence came a day after a top Nato general declared an end to Operation Medusa in the Panjwayi and neighbouring Zhari districts in Kandahar province. Lieutenant General David Richards, head of the 20,000 Nato-led force in Afghanistan, called the operation a "significant success". He said the insurgents had been forced to abandon their positions and reconstruction and development efforts would soon begin there.

Brigadier Ed Butler, commander of the British force in southern Afghanistan, has said his British troops had used at least 400,000 rounds of ammunition. "The fighting is extraordinarily intense. The intensity and ferocity of the fighting is far greater than in Iraq on a daily basis," he has said, adding that the battles were "close and personal and hand to hand".

The Guardian

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