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A bomb threat for London has been issued by Irish dissidents in the first coded warning outside Northern Ireland in 10 years, officials say.
Streets around the Mall were closed for five hours on Monday morning amid a major security alert.
BBC security correspondent Gordon Corera said: "My understanding is that this may have come because of a coded warning, which is why there is more concern about it than normal. Threats come in and out all the time.
"But if it was a specific code word warning, that would suggest something more serious and that would be why we have had this alert."
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