A man has been arrested after five mosques in Birmingham were vandalised.
Another man was detained by members of the public on Friday but later released, police said.
Windows were smashed with a sledgehammer at mosques across the city, with six windows smashed at one Islamic Centre alone.
A probe involving counter-terrorism officers was launched on Thursday after the attacks, which came just a week after 50 Muslims were shot in a mosque in Christchurch, New Zealand.
Police have now arrested a 34-year-old man from Perry Barr, and a 38-year-old man from Yardley.
A West Midlands Police statement said: “Two Birmingham men have been arrested this afternoon after five mosques had their windows smashed yesterday morning.
“A 34-year-old Perry Barr man handed himself into a Birmingham police station and was arrested on suspicion of racially aggravated criminal damage.
“A 38-year-old Yardley man was also arrested on suspicion of racially aggravated criminal damage this afternoon after being detained by members of the community. Both remain in custody this evening.
“The investigation continues by West Midlands Police supported by West Midlands Counter Terrorism Unit.
“This is a significant step forward in our enquiries however the investigation continues into the motive for the incidents.
“We are working extremely closely with mosques and local communities around the West Midlands and this will continue.
“It remains incredibly important that we unite together against those who seek to create discord, uncertainty and fear.”
The Yardley man, 38, was later released without charge and will face no further action.
A spokesman for the Witton Road Islamic Centre in Aston told the BBC that CCTV had captured a man smashing windows at around 1.30am.
"The whole of the front windows, about six, were smashed," he said.
"Because of the force he used it's gone through the windows and into the mosque itself."
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