A bomb left outside the Dublin offices of the energy giant Shell has been described as a “sinister development” by the company.

Irish Army bomb disposal unit carried out a controlled explosion on the device, which was discovered near the entrance to the offices of Shell E&P Ireland in central Dublin on Monday night.

Shell is building a controversial gas pipeline from the offshore Corrib gas field on Ireland’s west coast, during which there have been violent protests at Rossport in north County Mayo.

A policing operation, called Anvil, is estimated to have cost more than ten million pounds and Interpol’s assistance has been sought to identify protestors from abroad.

"The work currently being undertaken on the Corrib project has all the necessary consents and permissions required by the various statutory bodies which oversee the project," said a Shell spokesman.

"This is a time for calm assessment. We remain open and willing to talk to any individuals or groups who continue to have concerns about our project."

Terence Conway, a spokesman for the Shell to Sea campaign group, distanced protesters from the planting of the bomb. "We don't need any explosive devices. It's not what the campaign is about and will never be part of it,” he said.

"Despite how some have tried to portray us, we still seek a peaceful non-violent protest. The only device we have used in the past and will continue to use is the truth, it is the most powerful weapon we have."

A number of protestors were arrested last week during attempts to disrupt the work of a pipe-laying ship, which had to abandon the operation because of accidental damage to the vessel. It may now be delayed until the spring.

A woman protestor began a hunger strike last week and vowed to continue until the ship, the Solitaire, leaves Irish waters.

Mr Conway said he was suspicious about the planting of the device. “What we are fighting for is to get the truth out and if we were to plant devices like that, it would only distract from the issues," he said.

"The distraction from the issues only benefits Shell. That is what Shell consistently wants, to make something else the issue and deflect from what is happening."

The device has been handed over to investigating officers for further forensic examination.

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