(Reuters) - Britain has banned three foreign far-right activists from landing on its soil in the last three days, a British security official said.

In a Facebook posting on Saturday, Generation Identity, a British white supremacist group, said Austrian activist Martin Sellner and his American girlfriend Brittany Pettibone, a YouTube commentator and author, had been detained by the British government.

The British official said that when they landed at Luton Airport, north of London, on Friday, border police refused to allow Sellner and Pettibone to enter Britain and that they were detained and then deported on Sunday.

The official, who spoke to Reuters on the condition of anonymity, said the couple had been banned from entering by Britain’s Home Office on the grounds that their “presence in the UK was not conducive to the public good”.

On Monday, British border police stationed in the French port of Calais also denied entry to Lauren Southern, a Canadian right-wing activist. After being detained, Southern tweeted that British authorities had told her she was “officially banned from UK for ‘racism’”.

The official confirmed that British border authorities had denied Southern permission to enter Britain on the same grounds as the other two activists.

Southern was planning to meet Sellner and Pettibone in Britain, according to the conservative news website Breitbart. Breitbart also said Sellner had been planning to make a speech in London’s Hyde Park, but that papers served on him by the British authorities alleged the speech was likely to incite “tensions between local communities”.

Breitbart said Pettibone was blocked from entering Britain not only in relation to Sellner’s planned speech but also because she planned to interview Tommy Robinson, former leader of the far-right English Defence League.

Experts who monitor Britain’s far right movements said the government had recently stepped up efforts to keep out ultra-right-wing foreign activists.

Among other Americans who have been banned from Britain are anti-Muslim campaigners Robert Spencer and Pamela Geller, and Mark Weber, who heads a California group known for Holocaust denial.