As Britain's fallen soldiers come home, US warns of greater risks on road ahead

Unpublished Pentagon dossier reveals 'danger' of rushing Afghan withdrawal. Kim Sengupta reports

The bodies of six soldiers killed by a roadside bomb in Afghanistan, the highest number of British fatalities from one attack, were brought home yesterday; a sombre reminder of the dangers in the longest foreign conflict to involve this country since the Second World War.

The coffins carrying the remains of Sergeant Nigel Coupe, of the 1st Battalion, The Duke of Lancaster's Regiment, Corporal Jake Hartley, Private Anthony Frampton, Private Christopher Kershaw, Private Daniel Wade and Private Daniel Wilford, all of the 3rd Battalion, The Yorkshire Regiment, were flown to RAF Brize Norton for a private service and then taken to the John Radcliffe Hospital in Oxford.

Meanwhile in Afghanistan, comrades of the fallen soldiers continued on a mission reaching its final stages, with governments in the UK and the US facing growing public pressure to bring troops back early. However a US military report, seen by i, warns of the risks which will be posed by too hasty a withdrawal of troops and also points out the security pitfalls of the projected lowering of the Afghan forces' strength for cost reasons.

The discussion paper, drawn up by a Pentagon team, is in preparation for an international summit in Chicago in May which will shape the West's relationship with Afghanistan after the end of the combat mission in 2014. It looks at, among other issues, plans to cut the size of the Afghan forces by almost 40 per cent at the time they are supposed to be taking over security responsibility from Nato. It also examines the options for drawdown being considered by the White House, the most drastic of which would see a major reduction by next February.

The study points out that failure to establish governance in areas contested with the Taliban, with a return of corruption, would aid the insurgency.

There is widespread acceptance in London and Washington that Britain will follow the American lead in the timing and scale, proportionately, of the pull-out. While the two countries' leaders deliberate, Western officials are increasingly bemused by the latest "wild pronouncements" coming from a third, Hamid Karzai, in Kabul. He described the burning of Korans by US officials – a mistake – as "satanic acts that will never be forgiven".

Mr Karzai has also insisted that Nato hand over control of security to Afghan forces by next year. Under current US plans, these forces would shrink from 352,000 to 220,000 in the next 12 months, lowering the annual defence budget, which the international community will have to fund, from $6.2bn (£3.9bn) to $4.1bn. The US report says such a reduction is predicated on the insurgency trailing off.

A US official said: "Of course there will be significant savings by cutting numbers. But look at others costs. Why should Afghan soldiers and police risk their lives, essential if transition is to take place, if they know they will lose their jobs a little down the line? Also, do we really want 130,000 disaffected men, trained to use arms, made unemployed out on the streets, in an economy highly unlikely to find them other jobs? We need to be very careful what message we send."

The US will withdraw 22,000 of its remaining 90,000 troops this autumn. No decision, says the administration, has been made on when the rest will leave. Vice-President Joe Biden is said to want a rapid return, leaving specialist forces to carry out counter-terrorist operations. US and British commanders would like to keep as many troops on the ground as possible until 2014. General John Allen, the current head of international troops, insisted: "The campaign is sound, it is solid. It does not contemplate any form of accelerated drawdown." Chicago may show that to be wishful thinking.