A British government website responsible for pollution forecasts has been defaced by Islamist hackers in an apparent protest against the Iraq War.

The front page of UK-Air, which is run by the Department for Environment, Food & Rural Affairs (Defra), was replaced with a banner depicting the former Iraqi dictator Saddam Hussein, who was ousted during the war by the UK and US forces.

A message posted on the site by the Moroccan Islamic Union-Mail read: "It’s time to remind the British government what you did with Saddam Hussein will not forget.

"And we are ready to sacrifice with everything, as not to give up Iraq and stay alert for the coming [sic]."

Shortly after the site was brought down Defra UK-Air tweeted that it was aware of the problem, having been alerted to it by Jim McQuaid, an atmospheric scientist at the University of Leeds.

A statement posted to the site said: "The UK-Air website is currently offline. We are working to resolve this as soon as possible and apologise for any inconvenience."

As of Wednesday the site was still offline, though a splash page put up in the interim was displaying a pollution forecast.

The cyberattack coincides with a warning from the FBI that sympathisers of the terrorist group Islamic State, also known as Isis or Isil, are targeting WordPress sites in a bid to attract attention.

"Although the defacements demonstrate low-level hacking sophistication, they are disruptive and often costly in terms of lost business revenue and expenditures on technical services to repair infected computer systems," the bureau wrote in a public announcement.