A soldier guards people queuing at the UN office in Kabul

Large swathes of the country are under the control of warlords where people live under the daily threat of violence, said Christian Aid.

The charity, which is running aid projects in the country, wrote to Foreign Secretary Jack Straw warning him conditions were only getting worse.

Nato takes command of the International Security Assistance Force (ISAF) in the capital Kabul on Monday, but that security should be extended to the whole of the nation, says the charity.

And the push for a change in Nato and United Nations policy towards the war torn country should come from Britain, it adds.

Growing criminality is further compounding the insecurity felt by the Afghan population Martin Kyndt Christian Aid

"As we are sure you are aware, the security situation in Afghanistan has shown a marked deterioration in recent months," said the letter, which was backed by other aid agencies.

Only a properly trained Afghan National Army and police force can bring stability and security but they are years away, the agencies say.

"In the meantime, radical elements seek to undermine both the transitional government and the reconstruction process," the letter states.

"In addition, local struggles for power, fuelled in some areas by the opium trade, are leading to a growing fragmentation of the country.

Robberies

"While efforts to create a national army, police force and judiciary remain at an embryonic stage, the ongoing climate of impunity means that there is no protection for the individual from the arbitrary use of power.

"Growing criminality is further compounding the insecurity felt by the Afghan population; there are numerous examples of robberies, thefts and assaults even in (supposedly) one of the most secure regions, Herat."

The multinational Nato force should be in place before the next Loya Jirga gathering of tribal chiefs discusses a constitution in October, according to the agencies.

The letter was signed by Martin Kyndt, Christian Aid's acting director, along with AfghanAid's UK director Fraser Mackay, Care International UK's programme director Raja Jarrah, Ken Caldwell of Save the Children and TearFund's Graham Fairburn.