Image caption Arlene Arkinson went missing in 1994 and her body has never been found

The Northern Ireland Office has signed off on a bid to stop secret files from being accessed during an inquest into the death of a murdered schoolgirl.

Arlene Arkinson, a 15-year-old from Castlederg, County Tyrone, vanished in 1994 and police believe she is dead.

She was last seen with the convicted child killer Robert Howard.

Northern Ireland Office Minister Ben Wallace has approved a Public Interest Immunity (PII) application to withhold documents linked to the case.

The details were revealed at a preliminary hearing into the long-delayed inquest at Belfast's Laganside Court on Friday.

PII applications can be used when it is believed disclosure of state documents could be harmful to the public interest, such as concerns over national security or police informers.

However, the coroner will take the final decision on whether the PPI application will be granted.

Timeline - child killer Robert Howard

Analysis - BBC NI Home Affairs correspondent Vincent Kearney

This is an extraordinary development.

Public Interest Immunity certificates are normally granted in cases where there are concerns about national security.

They have been used many times in court cases during the Troubles.

Reasons given have included the protection of methods the police use to gather intelligence, and protecting the identities and lives of informers.

As far as I am aware, they have never been issued in a case like this one, the killing of a schoolgirl.

The Northern Ireland Office says it has agreed to a request from the PSNI for some information to be redacted, which means it would be blanked out.

We may never know precisely what sensitive information the police are seeking to hold back.

Coroner Brian Sherrard will hear legal submissions on the application on Tuesday and at least part of that hearing is likely to be held in secret.

Even when the coroner makes his ruling, he may not be able to say much about the reasons for his decision.

During Friday's hearing, a barrister for the coroner advised him: "You have to decide whether the materials should be released for the purposes of the inquest."

'Careful redactions'

Howard, who was the main suspect in the Arlene Arkinson murder investigation, died in prison last year aged 71.

Image caption Robert Howard was a suspect in the murder of County Tyrone teenager Arlene Arkinson but was found not guilty after a trial in 2005

In 2005, he was found not guilty of murdering the schoolgirl.

The jury was not informed during his trial that, by then, Howard was already serving life for raping and killing English schoolgirl Hannah Williams in 2001.

In a statement, a Northern Ireland Office spokesperson said: "At the specific request of the Police Service of Northern Ireland, some of the documents submitted to the court in relation to this inquest were subject to careful redactions.

"These related only to material the police judged would compromise their ability to bring murderers, rapists and other serious criminals to justice in future."