The United States has warned President Karzai of Afghanistan that international military and civilian operations are being paralysed by a police crackdown on private security guards carrying firearms.

William Wood, the US Ambassador to Kabul, met Mr Karzai on Sunday to ask him to intervene in the stand-off between the Interior Ministry and the booming private security industry, The Times has learnt.

The ministry said it was cracking down on unlicensed weapons and illegal security companies, but industry insiders accuse Afghan firms with links to the police - including one owned by Mr Karzai's cousin - of trying to steal their clients.

Afghanistan's security industry has grown from nothing in late 2001, when a US-led invasion toppled the Taleban Government, to a multimillion-dollar business, with 60 companies employing 30,000 people - 10,000 of them foreigners.

Humayun Hamidzada, a spokesman for Mr Karzai, confirmed the meeting with the ambassador and said that the issue would be resolved soon. But he gave no timetable and said that Afghan forces should eventually take over many of the responsibilities of the security industry. “We're working on an interim arrangement in order to allow the legitimate companies to operate,” he told The Times. “There is no double treatment for Afghan and foreign companies. But there has to be Afghan security over the longer term.”

The US Embassy declined to comment, but diplomatic sources fear that the issue could further sour relations between the international community and Mr Karzai, who has criticised British operations in the south and blocked the candidacy of Lord Ashdown of Norton-sub-Hamdon as UN “super-envoy” to Afghanistan.

Mr Wood's meeting came three days after Condoleezza Rice, the US Secretary of State, and David Miliband, the British Foreign Secretary, made a surprise visit to Kabul to try to mend fences with Mr Karzai.

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