Animal rights activists are being blamed for planting an incendiary device under a Sussex huntswoman's horsebox.

The firebomb failed to go off but police say it was potentially lethal.

The device was the second to be found on Saturday. Both were planted under vehicles belonging to members of the Old Surrey, Burstow and West Kent Hunt.

An extreme animal rights group, The Hunt Retribution Squad, had sent letters to seven hunt members telling them to stop hunting immediately or "non-compliance will result in every member and supporter of the hunt becoming a legitimate target."

An army bomb disposal team was called to the woman's home in Nutley, near Uckfield, after the device was discovered at about 6.15am on Saturday.

The bomb was last night being forensically examined. Inspector Steve Elridge of Sussex Police said: "It was capable of causing severe damage or even death and we are treating the incident as very serious.

"Fortunately it failed to activate. It is believed to have been left under the vehicle overnight."

Five hours earlier a similar device had gone off under the van of huntsman David Pitfield, 51, of South Nutfield, Surrey.

Inspector Elridge said: "No one has claimed responsibility for the attack at the moment. An investigation has been launched into the incident."

Mr Pitfield said: "It was a such a stupid thing to do. Innocent people could have been seriously hurt."

He said he received a threatening letter last week: "It said I was going to be in big trouble but it didn't say what they were going to do. I can't believe it was something like this."

Simon Hart, campaign director for hunting at the Countryside Alliance, said: "This vicious attack on members of this hunt is a clear indication that animal rights fanatics care little about human life."

No one has admitted responsibility for the attacks but seven members of the hunt received threatening letters on September 4, two days after hunt saboteur Steve Christmas was seriously injured while following a hunt at Horsted Keynes.

Trouble has since flared after hunt saboteurs claimed the 30-year-old protester was deliberately run over by members of the hunt.

Dawn Preston, spokeswoman for the Hunt Saboteurs Association, said: "Our name has already been linked to this alleged incident without a shred of evidence.

"The Hunt Saboteurs Association is dedicated to non-violent direct action against all bloodsports. But it still seems we are the first to take the blame when an incident like this occurs."