A suspicious package, later confirmed as a bomb, was found in an alleyway beside Aisha Mosque in Walsall by a member of the public on Friday night.
The West Midlands police confirmed that they were treating the incident as a hate crime and now its counter-terrorism unit was involved.
"The force is taking this attack against the mosque very seriously and we have a major investigation under way.
"At this stage we are keeping an open mind on a motive, but have recorded it as a hate crime. There is no evidence or intelligence to suggest that this is an act of terrorism," she added.
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Around 150 people were evacuated from their homes, and 80 had to stay in temporary accommodation in the Caldmore area of Walsall last night to allow bomb disposal experts to make the device safe.
"We have beautiful relationships with the local community and we've never had any trouble at all at our mosque.
We are not too worried about this and we have every confidence in the police," said Ziaul Haq, a spokesperson for the Aisha Mosque and Islamic Centre on Rutter Street.
Worshippers were allowed to return to the mosque for prayers on Sunday afternoon.
There have been at least 10 attacks on mosques across Britain in recent months.
The spike in these suspected Islamophobic incidents is thought to be a backlash to the murder of British soldier Lee Rigby on the streets of Woolwich in south-east London last month.