Hackers crashed the website of the National Crime Agency in an apparent revenge attack.

The site went down on Tuesday morning, days after the crime fighting organisation announced the arrest of six teenagers on suspicion of using a service created by a hacking collective known as Lizard Squad.

The group, which previously targeted Xbox and PlayStation networks, appeared to claim responsibility for the action.

A message posted on a Twitter account linked to Lizard Squad said: "Stressed out? http://www.nationalcrimeagency.gov.uk/ #offline."

It is thought the NCA website went down in a distributed denial of service (DDoS) attack, in which web servers or websites are flooded with massive amounts of data - leaving them inaccessible to visitors.

The crime fighting agency described its website as an "attractive target" and said attacks are "a fact of life".

A spokesman added: "DDoS is a blunt form of attack which takes volume and not skill.

"It isn't a security breach, and it doesn't affect our operational capability. At worst, it is a temporary inconvenience to users of our website.

"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.

"The measures we have in place at present mean that our site is generally up and running again within 30 minutes, though occasionally it can take longer. We think that's proportionate."

The website was back online after around two hours.

Last week the NCA led an operation targeting alleged users of a tool known as Lizard Stresser.

It is seen as a DDos for hire facility which gained notoriety among the hacking community after Lizard Squad claimed to have knocked Sony PlayStation and Xbox gaming services offline last Christmas.

None of those arrested in the most recent police activity are accused of involvement in those incidents, nor are they believed to be members of Lizard Squad.

The National Crime Agency (NCA) said they are suspected of maliciously deploying Lizard Stresser, having bought it using alternative payment services such as Bitcoin in an attempt to remain anonymous.

Organisations believed to have been targeted by the suspects include a national newspaper, a school, gaming companies and a number of online retailers. They have not been named and it has not been confirmed whether the attempted DDoS attacks were successful.

The arrests were made as part of an operation codenamed Vivarium, co-ordinated by the NCA and involving officers from several police forces.

Those arrested last week were an 18-year-old from Huddersfield, West Yorkshire; an 18-year-old from Manchester; a 16-year-old from Northampton; and a 15-year-old from Stockport.

Two other suspects, both 17, were arrested earlier this year. One is from Cardiff while the other is from Northolt, north-west London.

All six have been bailed, while a further two 18-year-olds - one from Manchester and one from Milton Keynes - were interviewed under caution.

As part of the same operation, officers are visiting around 50 addresses linked to individuals who are registered on the Lizard Stresser website - but who are not suspected of involvement in attacks.