FRESH police warnings were issued last night after the latest in a series of letter bomb attacks in the region.

The public were urged to be on their guard against the terrorism campaign, believed to be the work of animal rights extremists.

Yesterday, a bomb was sent to a pet supplier on the outskirts of Newcastle.

This is the seventh letter bomb to be sent to addresses round the country in the past four weeks, including four in Yorkshire and the North-East.

Officers declined to give further details of the family-run firm involved in the latest attack or the nature of the package, which was taken away by police for analysis.

The device failed to go off and no one was hurt, but police warned anyone working with animals to be wary of suspicious packages.

The Metropolitan Police Anti-Terrorist Squad has been called in, while detectives from Northumbria Police are liaising with officers around the country.

Detective Superintendent Chris Machell, of Northumbria Police, said: "Although we can't say for definite that the same people are responsible, we are speaking to other forces.

"We would have to suspect it is linked to some form of animal extremism, but no one has come forward to claim responsibility."

He added: "These devices are designed to cause serious injury and have the potential to kill. This is a message to the public and anyone who has the slightest links with animals to exercise extreme vigilance."

In December, a secretary at a company in Masham, North Yorkshire, that makes animal tags had a narrow escape when she opened a nail bomb at the wrong end and it failed to detonate.

Earlier this month, a 58-year-old farmer suffered facial injuries after opening a nail bomb at his farm in Ripon.

Meanwhile, security is to be stepped up at a North-East pharmaceutical plant after it was announced that it is to be targeted by animal rights protestors.

Members of Stop Huntington Animal Cruelty (Shac) announced yesterday that they plan to bring hundreds of supporters to protest outside the GlaxoSmithKline plant in Barnard Castle, County Durham.

Shac has no connection with the wave of bombings, but members have waged an intense protest campaign against Huntingdon Life Sciences laboratories in Cambridgeshire.

US investors have now propped up the ailing firm, which yesterday saw share prices soar by 13 per cent in the wake of the deal.

Shac's spokesman, Greg Avery, said yesterday the campaign would turn its attention to Glaxo, one of Huntington's main customers. He said: "We won't be targeting staff, because I'm sure many of them sympathise with us. Instead we want to let management know how strongly we feel.

"We will be moving the campaign North later next month and Barnard Castle will be one of those sites targeted."

Glaxo is the biggest employer in Teesdale, employing 1,500 workers at the 63-acre plant.

A spokeswoman at the plant said: "We have had protestors here before, and it has always been peaceful. But despite that, we will be informing staff of Shac's announcement and advising them to take extra precautions regarding security."