Pakistan announced on Thursday it was expelling 18 international charities amid growing paranoia that Western aid agencies are being used as a front for espionage.

It puts at risk more than $100m in assistance, according to an aid spokesman, and would affect millions of desperately poor Pakistanis.

The organisations include Saferworld, Plan International and International Alert, which are all based in the UK, as well as American and European groups.

Another 20 are at risk of expulsion amid a growing crackdown on international organisations operating in the country. Charity workers say they have faced increasing bureaucratic hurdles - including complications in obtaining visas and registration documents - without explanation.

Umair Hasan, spokesman for the Pakistan Humanitarian Foundation - an umbrella representing 15 of the charities - said those charities alone help 11 million poor Pakistanis and contribute more than $130 million in assistance.

"No organisation has been given a clear reason for the denial of its registration renewal applications," said Mr Hasan.