Militant anti-fracking protesters have been accused of using increasingly violent and intimidating tactics as they seek to disrupt drilling at a site in Nottinghamshire.

Staff at the Daneshill site operated by Australian company Dart have allegedly been attacked and racially abused by protesters as tensions escalate.

John McGoldrick, Dart Energy's chief executive, told the Sunday Telegraph: "We have recently witnessed an escalation in non-peaceful protest. Site personnel have been threatened with violence – death in one case – verbal abuse, racial abuse and now physical abuse.

"There is no way that the protest movement can claim it is making a peaceful protest. These abuses are despicable and cowardly."

In recent weeks, Dart say that protesters have stepped up their campaign.

On April 15, a group staged a 'blood moon' party, distracting site security and allowing a protester dressed as Robin Hood to break into the camp and scale and chain himself to a 15-metre high drilling rig.

Drilling was interrupted for seven hours before the man was arrested by police and subsequently released on bail.

Over the Easter weekend, protesters allegedly circled the site "screaming and shouting abuse, throwing objects at security personnel and causing criminal damage", Dart employees told the paper.

"We felt like we were under siege," said the source. "Things have turned very nasty."

The site manager claims that he was attacked by a 58-year-old woman whilst on his way to work one morning over that weekend. The woman was arrested and bailed by police.

Subsequently, a female security guard was allegedly threatened with death as she patrolled the perimeter of the site, and a guard of Somali origin racially abused.

Dart said that incidents had been reported to the police, and it would press for the "fullest charges" to be brought against those responsible.

Nottinghamshire police acknowledged that there had been a spate of recent incidents at the site.

Superintendent Mark Pollock, of Notts police, said: "We recognise environmental issues are emotive but our role as police is clear – we are here to protect life, prevent crime and maintain peace.

"Where there are any assaults, threatening or abusive behaviour or criminal damage we will take action against the offenders."

Anti-fracking groups claim that isolated incidents are being used to discredit legitimate protests.

Peter Kennedy, of Frack Free South Yorkshire, said: "We are committed to peaceful, non-violent protest against the long-term health and environmental impacts that unconventional gas extraction will inflict on our local communities.

"Violence, threats and racial prejudice are absolutely not tolerated – anyone who does not conform to the camp's non-violent principles is asked to leave. It is this strict zero tolerance policy that has facilitated such light touch policing of the protests."