Suspect packages sent to Army offices in England are understood to have contained explosive black powder and to have been sent from the Republic of Ireland.In a statement on Monday, Scotland Yard said: "We are aware of the claim of responsibility for the devices that were sent to Army recruitment centres in England last week."The claim was received on Saturday 15 February by a Northern Irish media outlet using a recognised codeword. The claim was allegedly made on behalf of the 'IRA'."The public is urged to remain vigilant and report anything suspicious to the Anti-Terrorist Hotline, 0800 789 321."According to the Irish News, the group's admission also came with a warning that attacks "will continue when and where the IRA see fit".Last week, senior police sources told UTV that the 'New IRA' sent the devices to the armed forces offices in Oxford, Reading, Chatham, Aldershot and Canterbury.A total of seven parcels were mailed - four were intercepted on Thursday, in addition to three which were found earlier in the week.A shopping centre in Slough also received one of the potentially explosive parcels.A Number 10 spokeswoman described them as "crude", but said injuries could have been caused.