Imams and Islamic scholars from around the UK gathered at London Bridge on Wednesday to lay flowers close to the scene of Saturday's terrorist attack.
A statement – said to have the support of 500 UK imams – was read out to the large gathering.
Imam Qari Asim, spokesperson for the British Muslim Forum and Imam of the Leeds Makkah mosque, said: "We want to send a clear message to any Muslim attracted to violent extremism.
"This is forbidden by your religion. There is no justification in Islam for taking innocent life. If you follow this path you are stepping away from Islam to a dark and godless place.
"Your views are not welcome in our mosques or in our communities. This is not a path to heaven – think of the pain you will cause, the lives you will destroy. Please, think again."
Christian and Jewish leaders – including Anglican Bishop of Southwark Christopher Chessun – also attended the event to show their solidarity.