Two Britons and two Afghans have been detained for carrying dozens of AK-47 assault rifles in the Afghan capital, police said on Wednesday, in what appeared to be the latest flare-up in tensions between the government and private security firms.

Kabul police chief Ayoub Salangi said the four men were illegally carrying the weapons, along with plenty of ammunition, in the eastern part of the capital where there are several foreign military bases.

Some of the weapons did not have serial numbers or (the numbers) had been removed, Salangi told Reuters,. He said the 30 rifles belonged to a foreign security firm in Kabul.

We asked the company to show their licence but they are yet to do so, Salangi said, adding investigations were under way.

Dozens of private security firms were set up in the years after the Taliban government was toppled in late 2001, providing security for businesses, embassies, aid projects and government offices.

In August 2010, Afghan President Hamid Karzai said he wanted private security firms -- with the exception of firms whose guards work inside compounds used by foreign embassies -- to close by the end of that year.

The deadline was later pushed back to March 2012.

Karzai has frequently said the security firms were the biggest barrier to the development of local police forces across Afghanistan. They have also been accused of acting with impunity and putting ordinary Afghans at risk with often heavy-handed tactics.

It is intended a branch of the police, the Afghan Public Protection Force (APPF), will take over the work done by private security firms, a process which has begun, but some in the industry do not believe the APPF will be ready in time.

Foreign forces in Afghanistan are in the process of handing control of security over to the Afghan army and police, with foreign combat troops due to leave by the end of 2014.

(Reporting by Hamid Shalizi; Editing by Amie Ferris-Rotman and Paul Tait)