A Police investigation is under way after a group wrote to the Echo claiming responsibility for vandalising Labour councillors' cars and arson attacks on an Islamic centre.

Forensic tests are being carried out on a handwritten letter posted to the Echo offices in Basildon.

The writer claims to be part of an unnamed group responsible for two arson attacks on the Triangle Community Hall, in High Road, Langdon Hills, and paintstripper being hurled over four councillors' vehicles outside their homes at Laindon and Fryerns. It said they were a "direct retaliation" to alleged rapes of women in Hadleigh and South Woodham Ferrers. The letter, posted with a second-class stamp and a Southend postmark, blamed the alleged rapes on members of ethnic minorities.

It went on to threaten further and more serious attacks against organisations that support multiculturalism.

Supt Glenn Caton of Basildon Police said the letter was being treated seriously and as racist. He said it was the first "substantial lead" since the strikes on the councillors' cars. He said: "A letter of this nature always has to be taken seriously. It is now in our possession and we are carrying out forensic examinations.

"There was no natural link between the attacks but the letter provides one and we can never discount any line of inquiry. We appeal to the writer to contact us or anyone who believes they know someone who may have written it to get in touch."

Mr Caton said the threatening tone and racist content was worrying but it is possible it was not written by those responsible for the attacks.

He said: "We have to take any talk of threats seriously but hope our investigations prove it as otherwise."

An 18-year-old girl was allegedly raped on Salvation Army farmland in Hadleigh on May 8. A 15-year-old girl was raped in a skate park in South Woodham Ferrers on May 13. Two separate men have been charged with the unconnected offences and are going through the courts.

The Islamic centre was struck by firebugs on May 21 and a few days earlier. Labour councillors Phil Rackley, Allan Davies, Paul Kirkman and Swatantra Nandanwar suffered damage to their cars overnight on June 2.

Mr Rackley said: "There is no way we will change our beliefs and our fight for the rights of people. If they really believe what they are saying they should have the guts to come forward and give their names."

l Anyone with information should call the divisional investigating officer on 01268 532212.