An investigation has begun into a potential electoral fraud in an east London borough, the Metropolitan Police (Met) has said.
The Electoral Commission has alerted the Met about "potential fraudulent registration of voters" in Tower Hamlets.
Police are also investigating another allegation in connection with a recent by-election held in the same borough.
On 3 May, voters will elect the mayor and London Assembly Members.
A statement from the Met said: "On the afternoon of 26 April, the Metropolitan Police Service (MPS) received an allegation from the Electoral Commission relating to potential fraudulent registration of voters in Tower Hamlets.
"We are currently investigating this allegation plus a further allegation of offences linked to a recent by-election in Tower Hamlets received on 28 April.
"All allegations of electoral fraud are assessed, and where appropriate, thoroughly investigated by officers from MPS Specialist Operations, in close liaison with local authorities, the CPS and other relevant agencies."
A statement from Tower Hamlets Council said: "We work to the full extent of our powers to ensure the electoral register is as accurate as possible - in fact we conducted extra visits to over 4,700 electors in the days before the register closed.
"As a result, we removed 890 electors from the list as they had moved on.
"However, it is important not to confuse fraudulent activity with a register that changes by up to 20% a month because we have a population that is highly mobile - our borough includes a high proportion of students and restaurant workers."
Both the police and the council appealed to residents to report any suspicious activity.