PRESS ASSOCATION -- The Taliban attack on the British Council offices in Kabul has underlined the failure of the western strategy in Afghanistan, the UK's former special envoy to the country has warned.

Sir Sherard Cowper-Coles said claims Afghan forces would be able to take over responsibility for security after 2014 - as Britain and America are planning - had been exposed as a "fantasy".

Once international forces pull out, he warned the country would be plunged into a bloody civil war - in which the rival parties "fight themselves to a standstill" unless there was a political settlement with the Taliban.

"The strategy is not working. It is a fantasy to imagine that the Afghan security forces are going to be able to secure Afghanistan any time these ten years. They won't be able to secure Afghanistan unless there is a new political and regional settlement," he told the BBC Radio 4 Today programme.

"If Hillary Clinton was doing her job properly as America's chief diplomat she would be bringing together the regional foreign ministers and saying it's Ramadan, it's the Muslim holy month, we should be bringing this ridiculous violence to an end.

"It is about talking to all the regional powers, it is about talking to all internal factions and bringing them all together in an Afghan-style peace process. It will be messy, it will be difficult but the military approach is clearly not working."

Sir Sherard, who has been an increasingly outspoken critic of US policy in Afghanistan since leaving the Foreign Office, said the Americans needed to take the lead in finding a settlement.

"There is a deal to be done but it needs leadership by the United States and the United Nations, its needs imagination, and above all it needs political courage and political will in Washington," he said.

Taliban suicide bombers killed at least eight people, including a New Zealand special forces soldier and three Afghan security guards, after storming the British Council's offices.

Foreign Office minister Alistair Burt said he was "deeply saddened" by the soldier's death, and thanked New Zealand for its role in bringing the "dreadful incident" to an end.