A group of foreigners, including nine Britons, who were arrested in China are suspected of distributing "terrorist videos", local officials have said.

Six of the Britons were deported and have now returned to the UK, the Foreign Office has said.

The three other Britons and two people with joint UK-South African nationality are understood still to be in custody.

They were in a group on a tour of ancient China when they were held on 10 July at Ordos in Inner Mongolia.

The Foreign Office has requested an explanation for the group's detention and has sought assurances about their treatment and the conditions in detention.

Gift of the Givers, a humanitarian relief organisation based in South Africa, said none of the group had been charged.

'Violent terrorist videos'

Zhang Xi, an official in Ordos in charge of dealing with foreigners, said: "These people are suspected of watching and spreading violent terrorist videos and were arrested last Friday."

They have been visited by the British consulate, the official added.

The group of 20 who were arrested comprised 10 South Africans, nine Britons and one Indian.

Of the 10 South Africans who were arrested five have since been released, the BBC understands.

The other five are still in China and include two doctors and a veteran of Umkhonto we Sizwe, the armed wing of the African National Congress.

This group of three are all related to the CEO of Vodacom - the African mobile communications subsidiary of Vodafone - Shameel Joosub.

China Odyssey Tours, a travel agency based in China, said the group had been on one of its tours.

In a statement on its Facebook page Gift of the Givers said the tour went "horribly wrong" when the party was arrested at Ordos Airport.

The charity said representatives from the British, South African and Chinese governments met on Tuesday to secure the release of 11 of 20 people being held, but no formal charges had been put to any of those detained.