WASHINGTON (AFP) - The United States Federal Bureau of Investigation (FBI) is investigating a string of hacks that defaced US websites with imagery from the Islamic State in Iraq and Syria, NBC News reported on Monday.

Websites including a racecar speedway in the state of Ohio, a Goodwill centre in Missouri and a church in Canada were defaced with the radical group's black flag, the news organisation reported.

Attacks against similar low-profile websites were also recorded in Montana, New York, Massachusetts and Minnesota.

The FBI said it was aware of the incidents and "is contacting the impacted parties". A security analyst told NBC it was unlikely the hacks had any "real connection" to ISIS group.

The ISIS-themed hacks were on Sunday reported in Ireland, where the Dublin Rape Crisis Centre in Ireland's website was defaced.

"Hacked by Islamic State (ISIS) We Are Everywhere," the hacked website said while playing music associated with the group.

ISIS has relied on an aggressive propaganda campaign online to appeal to possible recruits to join and support the violent Islamists in Iraq and Syria.