A major counter-terrorism operation goes on today after suspected explosive devices said to bear the hallmarks of Northern Ireland-related terrorism were sent to Army careers offices in Canterbury and Chatham.

Dissident Irish Republican terrorists are being blamed on a spate of suspect packages - with the devices described as crude but "viable" and having the potential to injure.

No specific group has claimed responsibility, but one of seven packages sent to recruitment centres across the south east was stamped with a Republic of Ireland postmark.

Royal Mail and military staff are now being told to be extra vigilant and screening procedures for mail to recruitment centres are now being reviewed.

The discovery at Canterbury's Army careers office in St Peter's Street yesterday came two days after a "basic, but viable explosive device" was found by military recruiters in Chatham.

Prime Minister David Cameron yesterday chaired a meeting of the Cobra crisis committee to discuss the government's response to the threats.

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Last night, a Downing Street spokesman said: "Seven suspect packages have been identified as containing small, crude, but potentially viable devices bearing the hallmarks of Northern Ireland related terrorism.

"These have now been safely dealt with by the police and bomb disposal units.

"Guidance has been issued to staff at all military establishments and Royal Mail asking them to be extra vigilant and to look out for any suspect packages..." - Downing Street

"Guidance has been issued to staff at all military establishments and Royal Mail asking them to be extra vigilant and to look out for any suspect packages and the screening procedures for mail to Armed Forces Careers offices is being reviewed."

The alert was raised at Canterbury's city centre Army careers office yesterday afternoon.

Three other suspect packages were discovered at Army recruitment centres in Slough, Oxford and Brighton.

On Wednesday, a package was delivered to an Army recruitment office in Aldershot, Hampshire.

And explosive devices were found at Army offices in Dock Road, Chatham, and Reading on Tuesday.

Bomb disposal units from the Ministry of Defence arrived at the Canterbury office to assess the contents of the package.

Officers set up a large cordon down St Peter's Street and shoppers were being told to avoid the area.

The cordon was reduced shortly before 3pm, but a team from the Royal Logistic Corps and police remained at the scene until shortly before 5pm.

Video: Police and MOD experts at the scene in Canterbury

Kent Police spokesman Jane Walker said: "Police were called to St Peter's Street at midday to reports of a suspicious package at the Army careers office.

"Police at the scene have set up a cordon, and are investigating."

Earlier, KentOnline reporter Alex Claridge said: "There are lots of people milling about at the end of St Peter's Street, which is where police have closed the road.

"There is a police car and a police van. And now a counter-terrorism unit has arrived."

"The contents of the packages are suspicious in nature and will now be sent off for forensic examination..." - Det Supt Stan Gilmour

The South East Counter Terrorism Unit is investigating the multiple reports of suspect packages at Army careers offices.

Det Supt Stan Gilmour said: "The contents of the packages are suspicious in nature and will now be sent off for forensic examination.

"Even if the contents are determined to be a viable device they pose a very low level threat and are unlikely to cause significant harm or damage.

"When a suspect package is reported we have a routine response which means we may need to evacuate the area if necessary until we can be sure it poses no threat to the public.

"Whilst this can cause concern and disruption for local communities, it is a necessary precaution until we know what we are dealing with."

He added: "Because suspicious packages were found at various locations, notes were sent out to all the Army Careers offices as well as the Post Office asking staff to be extra vigilant and look out for any suspect packages."

A Ministry of Defence spokesman said: "The relevant police authorities are investigating with military EOD (explosive ordnance disposal) teams in support and any further inquiries should be directed to the police.

"Security advice has been reiterated to our personnel."

In Canterbury, traders were told to shut up their shops and move away from the scene.

Revivals clothes shop owner Debbie Barwick said: "The police came in and told us to shut up the shop. It looks like a bomb hoax."

Teenager Reece Hirst was being tattooed at Third Eye near the Army careers office when he was told to leave.

The 18-year-old said: "I was having my tattoo done when suddenly the shop owner shouted for everyone to get out.

"We were told it was a bomb scare and we had to wait out here. I keep getting pushed further back. I don't know what’s going on – I'm just waiting because I need to get my tattoo finished."

Fellow witness Jamie Roberts said: "It was just a normal day and I was having a fag outside when the police turned up. They went running in saying everyone had to get out."

The Canterbury scare came two days after suspect packages were delivered to Army careers offices in both Chatham and Reading.

Bomb disposal experts were called to Chatham town centre after the discovery of the envelope at about 11am on Tuesday.

The office was evacuated and police cordoned off the scene around The Brook.

A bomb disposal unit arrived soon after and witnesses reported seeing one of the crew members entering the building by a back door at about 12.30pm.

The area reopened at about 5pm after the package had been "made safe".

A similar package was delivered to an army recruitment centre in Reading on Tuesday and officers are investigating whether the two incidents are related.

A Ministry of Defence spokesman earlier said: "We can confirm that we are aware of suspicious packages discovered yesterday at two Armed Forces careers offices in Chatham and Reading.

"The relevant civilian police constabularies investigated, with military EOD teams in support, and any further inquiries should be directed to the police. Security advice has been reiterated to our personnel."

The drama in Canterbury echoes scenes in August 2011, when two parts of the city centre were shut down due to bomb hoaxes.

Two suspect packages sparked evacuations in the areas surrounding Old Dover Road and St George's Street.

Police released CCTV images of a suspect in the days that followed, but no one was ever held responsible for the scares.

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