A threatening video targeting a London councillor has been posted on the web.
Abbey Mills mosque will be able to accommodate 12,000 people
Alan Craig, who represents Canning Town South ward, east London, said the video was an "extremely sick joke" and he has informed police.
Mr Craig, 61, has opposed plans to build the UK's biggest mosque, Abbey Mills mosque in West Ham.
A Metropolitan Police spokesman said: "Officers will view the video in due course to ascertain whether any criminal offences have been committed."
Islamic group Tablighi Jamaat plans to build a 12,000 capacity mosque on land in West Ham, close to the Olympic Park site.
Speaking to the BBC Mr Craig, a member of the Christian Peoples Alliance on Newham council, said a friend brought the video to his notice a week ago.
The video, which includes pictures of the councillor, his wife and young daughters, was posted by a 23-year-old Muslim man from Stevenage.
Mr Craig said: "I thought it was pretty awful. If its a joke, its an extremely sick joke, especially putting my children up on it."
He said he registered a case with the Forest Gate police station on Monday.
"I refuse to be intimidated and I intend to get on with my life and the opposition to the mosque. You can't live in fear," Mr Craig added.
A spokesman for Abbey Mills mosque said: "We are not responsible for the content of external websites. But we condemn totally anyone who incites violence.
"If this has been reported to the police then it is right that they should investigate it."
Tablighi Jamaat has appointed architects Allies and Morrison, whose previous projects include The Royal Festival Hall, to build the mosque.
The mosque is still at a design stage and is estimated to cost between £50m to £75m, a spokesman for the mosque said.
Mr Craig said he is not opposed to plans to build the mosque but said he does not approve the group behind the project, which he describes as being a "separatist and isolationist" group.
In July an online petition against the construction of the mosque put up on the Downing Street website was signed by more than 255,000 people.
Then London Mayor Ken Livingstone said the petition was part of a "vicious" campaign to spread untruths about the scheme.