Image caption Armed police were called to the technology college on Friday afternoon

Police mounted a major operation to protect pupils at a Merseyside school after they were alerted by the FBI.

Armed police were called to St Aelred's Catholic Technology College in Newton-le-Willows on Friday after reports someone had made threats to kill there.

The United States' Federal Bureau of Investigation raised the alarm after picking up a threat posted on social networking site Facebook.

A 19-year-old man was arrested and later released on bail.

More than 1,000 students, some of them taking their GCSEs, were in the Birley Street school at the time of the alert.

All entrances and exits were sealed while police investigated.

'Leaving this world'

The school said it was the FBI who raised the alarm after internet scanning software picked up a suspicious combination of words.

It picked up a posting showing a picture of a gun being held above a scrawled note, which read "tomorrow - last day of school" and went on to mention bullies and "leaving this world".

Headteacher Edward Marr has now written to parents explaining how the situation came about.

He wrote: "Police officers attended school at 0800 am on Friday morning. They had a photograph from the internet and asked if I could identify a person on it.

"It emerged that a threat had been made against the school which had been picked up by the FBI in America and passed eventually, as the school was identified, to Merseyside Police.

We were able to deal with the threat well away from the school premises Ch Supt Chris Armitt, Merseyside Police

"Staff at the school were able to suggest the identity of the man on the photograph and an arrest was made."

Some parents have criticised police over why their children were allowed into classes while officers were investigating a possible armed threat.

Ch Supt Chris Armitt, from Merseyside Police, denied suggestions that officers could have closed the school as soon as they were aware of the threat.

He said: "We received some information between 1am and 2am, that information was imprecise and what we had to do was clarify what the information meant and what it related to.

"Once we were able to identify that school as potentially being at risk, we took steps quickly to get with the school staff."

He added: "They were able to help us identify the possible threats that we faced and we were then able to deal with that well away from the school premises."