Police have arrested a man after several schools across West Yorkshire implemented lockdown measures following a threatening email.
Schools in Leeds and Bradford sent messages to parents on Thursday informing them that pupils were being kept indoors after they were advised of the threat by the city council.
West Yorkshire Police said the contents of the email were being investigated and reassurance and safety advice were being offered to affected schools.
A spokesperson said: "Officers have commenced an investigation into a potential malicious communications offence and have now made an arrest in connection with the matter."
Parklands Primary School, Beeston Primary School, Sharp Lane Primary School, Windmill Primary School and Rodillian Academy in Leeds were among those to issue notices to parents via social media.
Beeston Primary School posted on Facebook: "Following information from Leeds City Council health and safety team about a credible threat to all schools in Leeds, Beeston Primary School has ensured that any necessary precautions in school have been made.
"All gates remain closed and locked, as usual, and staff are being extra vigilent. We have well rehearsed procedures for lock down in place should we need them and a robust CCTV system covering all school grounds which is being closely monitored."
The school had received no direct threat and the children and staff were safe, it said.
In an email to parents, Rodillian Academy principal Lorraine Bradley said: "We have closed the perimeter gates after advice from Leeds City Council for precautionary reasons, and have been asked not to admit anyone to the site without thorough safeguarding checks.
"I cannot stress enough that there has been no incident within the school and no specific threat to Rodillian Academy. This advice has gone out to all schools and colleges across the city."
Windmill Primary School implemented "invacuation measures" and would keep windows and doors closed all day.
West Yorkshire Police said the force had not told schools to lockdown and had not stated the threats were credible.
A Leeds City Council spokesperson said: "We are aware of an ongoing situation relating to threats made towards a number of schools in Leeds and we are working closely with West Yorkshire Police to monitor the situation and provide support to schools."
Earlier this week, Humberside Police said hoax threats had been made to schools in the Hull area.
A police investigation was also launched after malicious emails were sent to a number of schools in the North West.
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