Two British journalists working for Iranian-owned Press TV have been arrested in Libya.

Reporter Nicholas Davies and cameraman Gareth Montgomery-Johnson were detained by members of the Misrata Brigade on Tuesday and are being held in Tripoli.

Mr Montgomery-Johnson's sister Melanie Gribble says she has no idea why her brother, from Carmarthen, was arrested and she is concerned for his welfare.

The Foreign Office confirmed that two British nationals have been detained.

Press TV says on their website Mr Davies and Mr Montgomery-Johnson were seized along with two Libyan nationals and it has not been in contact with the four since Tuesday.

It is something he was very passionate about doing. He is just trying to document what was going on. Melanie Gribble, Sister of Gareth Montgomery-Johnson

Ms Gribble, said the family found out about Mr Montgomery-Johnson's detention by accident, after a friend posted a link on Facebook.

She told BBC Radio Wales the Foreign Office confirmed the arrest but could not give any further information."

She said her brother had just returned to Libya after a two-week break to relax after working in the country since July last year.

In August last year, Mr Montgomery-Johnson spoke to Radio Wales about his work in Libya.

Ms Gribble said: "It was something he is very passionate about doing. He is just trying to document what was going on.

She said that she knew her brother was well "25 hours ago" but had received no word about him since.

Libyan leader Colonel Muammar Gaddafi was overthrown and killed last October, eight months after the start of protests and an uprising.

The transitional government has been struggling to control armed militias since the revolution.