Four people arrested as part of an investigation into two attempted letter bomb attacks on Army offices in Kent have been released.

Two men and two women were held by police in Londonderry, Northern Ireland, last Wednesday morning.

Devices were sent to Army recruitment offices in Canterbury and Chatham in suspected IRA-linked attacks in February - as well as elsewhere in England and Northern Ireland.

The four were questioned by officers from the Police Service of Northern Ireland (PSNI) before being released without charge.

The men - aged 35 and 46 - and women - aged 21 and 44 - were arrested in the city and taken to the serious crime suite at Antrim police station for interview.

A police spokesman said the investigation is being led by detectives from the PSNI serious crime branch, which has been working with officers from the South East Counter Terrorism Unit in England.

Anti-terror police found a device at the Army careers office in Canterbury on Thursday, February 13 - two days after another was delivered to a centre in Chatham.

Others were delivered to Brighton, Oxford, Slough, Aldershot and Reading.

They were described as being "crude" in design, but having the potential to injure.

A major counter-terrorism operation was launched and Downing Street said the packages had the hallmarks of "Northern Ireland-related terrorism".

The first of seven suspect packages delivered to military recruiters was sent to the Army careers office in Dock Road, Chatham, on Tuesday, February 11.

Bomb disposal experts from the Ministry of Defence were called to the town centre and evacuated the office. After several hours, police said the device had been "made safe".

Then Canterbury was at the centre of another bomb scare at about midday two days later.

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

A team from the Royal Logistic Corps left after around five hours and the device was sent off for forensic tests.