Two men have been arrested under the Terrorism Act in connection with explosions near two mosques.
A "loud bang" was heard near the Aisha Mosque, in Rutter Street, Walsall on 21 June while a second explosion happened near Kanzul Iman Masjid mosque in Tipton on Friday.
The men, aged 25 and 22, are described by police as Eastern European.
A Wolverhampton mosque has also been been evacuated after reports of "a possible device activation" last month.
Police received the information about the incident on 28 June at Wolverhampton Central Mosque, Waterloo Road, as part of their investigation into the explosions in Walsall and Tipton.
The building and surrounding area was evacuated at about 20:00 BST.
Specialist and local officers are expected to remain at the scene throughout the evening.
A military bomb disposal team is in attendance and a number of roads have been closed.
'Suspect forced down'
Earlier army bomb disposal experts were at an area near Talbot Way, Small Heath, Birmingham where some properties were evacuated.
The pair were arrested on suspicion of being involved in the commission, preparation or instigation of an act of terrorism.
The first suspect was arrested after being spotted by officers in the local area. The other man was arrested at a nearby property.
Assistant Chief Constable Marcus Beale, from West Midlands Police, said: "I would like to thank the public for their ongoing support and the way in which they responded to our appeal.
"I appreciate that there is significant disruption whilst experts search and check this area. These road closures are essential to ensure that we keep everyone safe.
"Investigations like this are complex and we need to ensure that we obtain every piece of information or forensic evidence possible."
One eyewitness told BBC WM about 100 people had initially been evacuated from businesses close to the area being searched.
Embreen Hashmi said: "All of a sudden there was an entourage of police and they cordoned off the whole business park and everybody had to come out on to the street.
"We weren't sure what it was and everybody was saying that it was some sort of bomb scare which frightened us.
"When we spoke to people that worked in the same building as one of the suspects he said there was a chap that they used to work with and that he was actually being forced down by armed police and they had to evacuate the building."
Police were called to the mosque in Walsall the day after the explosion was heard after a member of the public discovered debris from a device.
A 75-year-old man from the town was arrested last month but has since been eliminated from enquiries.
The other explosion was on a disused railway line near Binfield Street in Tipton last week.