A group of hackers on Tuesday claimed they had downed the website of Britain's lead law enforcement agency after it arrested six people over similar attacks.

The National Crime Agency (NCA) website was offline for around an hour after suffering a Distributed Denial of Service (DDoS) attack, claimed by hacking group Lizard Squad.

On its Twitter page, the group posted the message: "Stressed out? http://www.nationalcrimeagency.gov.uk/ #offline", superimposed with the NCA logo.

A DDoS attack cripples the target website by barraging it with automated requests from many different sources, making it almost impossible to prevent.

The NCA called the attack a "temporary inconvenience" and denied it was a security breach.

"The NCA is an attractive target," it said in a statement.

"DDoS is a blunt form of attack which takes volume not skill. It isn't a security breach and it doesn't affect our operational capability."

Given the cost of trying to repel such attacks, the agency claimed that its current measures were "proportionate".

"We have a duty to balance the value of keeping our website accessible with the cost of doing so, especially in the face of a threat which can scale up endlessly," it added.

The attack came four days after the NCA arrested six hackers, accusing them of buying code from Lizard Squad that enables DDoS attacks.

The code is believed to be behind attacks on the Microsoft and Sony games networks last year.

Following Friday's arrests, Lizard Squad warned it would respond, tweeting: "Due to the recent raids, we're going to start operations back up again. Expect more soon."

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