(Reuters) - A British drug user has died from anthrax, health authorities said on Friday, triggering concerns a European outbreak of the rare infection among people who inject heroin may be worsening.

The user was possibly infected by contaminated heroin and there were at least seven other similar cases across Europe, the Health Protection Agency (HPA) said in a statement.

"It's likely that further cases ... will be identified as part of the ongoing outbreak in EU countries," said the HPA's Dilys Morgan.

The HPA, set up to guard against infectious diseases and environmental hazards, said anthrax in drug users was very rare.

An outbreak of infections in 2009/2010 in Europe was also traced to contaminated heroin, but before then, only one case had been reported, in Norway in 2000.

From June 2012 there have been new cases of anthrax among heroin users in Europe - three in Germany, two in Denmark, one in France and one in Scotland, the HPA said.

"It is unclear as yet whether this (death) and a case in Scotland at the end of July are linked to the outbreak in Europe but the HPA will continue to monitor the situation," it added.

No further details were available on the British victim, who died in hospital in Blackpool, northern England.

Anthrax is a fairly common bacteria whose spores can be used as a biological weapon.

Humans are rarely infected. But if the spores are inhaled, the infection can take hold quickly and by the time symptoms show, it can be too late for successful treatment with antibiotics.

Anthrax infection is not transmitted directly from one infected person to another. It can come in several forms, including skin anthrax, lung anthrax - which has a 75 percent death rate - and gastrointestinal forms that can progress to blood infection and death.

(Reporting by Kate Kelland and Stephen Addison; Editing by Andrew Heavens)