Scotland Yard has begun investigating after the "wanted-style" posters came up in Tooting in south west London, the Independent reported.A fatwa - a religious ruling in Islamic law - can be, but is not always, interpreted as an incitement to kill, the daily said.
A Scotland Yard spokesman said: "Police are aware of a number of posters in the Tooting area. We are liaising with the local authority to get them removed. We are also working to find out who put them up."
Tooting MP Sadiq Khan said the posters were "offensive, divisive and unlawful".
"Whoever is behind it should not only face the full extent of the law, but should also foot the bill for damage caused to public property and the cost of taking down these inflammatory posters," he said.
"Tooting is a vibrant, diverse and welcoming place and I take very seriously any attempts by anyone who tries to destabilise our community," he added.
Jailed Islamic clerics include Abu Hamza, 52, who was imprisoned for seven years in February 2006 for inciting murder and race hate. He is challenging attempts to extradite him to the US on terror charges.