A 35-year-old man has been arrested after a headless torso feared to be EastEnders actress Gemma McCluskie was dragged from Regent's Canal in east London, sources said today.
Sky News and the BBC reported that the man arrested is her brother, Tony McCluskie.
But the Met Police said they could not confirm or deny the report.
PA reported only that the man being questioned was understood to be known to McCluskie, who is single. Detectives said the suspect remains in custody at an east London police station.
Relatives and co-stars of Miss McCluskie, 29, were said by a PA source to be "fearing the worst" as Scotland Yard carried out forensic tests on the remains.
McCluskie was last seen on Thursday 1 March in Bethnal Green.
She played Kerry Skinner in 30 episodes of EastEnders in 2001, and also appeared in children's TV programme North and South.
The female torso was discovered close to Hackney's famous Broadway Market at 2.40pm yesterday, the Metropolitan Police said.
The unclothed body's arms, legs and head had been hacked off before it was found floating in the waterway, a source told the Press Association.
"At this early stage officers believe they know the identity of the victim but must await further forensic tests before formal identification can take place," a spokeswoman said.
"Police were initially contacted by a member of the public who had noticed something suspicious floating in the water.
"The torso was recovered by divers from the Met's Marine Support Unit (MSU) and additional searches are due to be carried out in the water."
A post-mortem examination was taking place at Poplar Mortuary as an incident room was opened in Barking.
Detective Inspector John Nicholson is leading the murder inquiry.
A female neighbour of Miss McCluskie, who did not give her name, fought back tears as she said: "I'm so shocked, this is not something you hear about every day.
"I've seen her about four or five times, just to say hello to, we never talked that much.
"I didn't realise she'd gone missing - and now I am hearing this."
McCluskie was wearing a mustard coloured top and blue leggings when she went missing without contacting friends or family. Police said the disappearance was "out of character".
Around 100 people joined a search to look for her on Monday evening.
The hunt, which was organised by her cousins Kyri Sambridge and Nikki Tsindides, stretched from the East End to South London in an attempt to find any information about her whereabouts.
They distributed leaflets with her picture and information, and spoke to shopkeepers and locals about where she was last seen.
Kyri, 27, told London24: "We got an important clue when we went into a kebab shop on Hackney Road, two minutes from where she lives. They told us she came in there at 8pm last Thursday.
"Until then the last time she had been seen was in the afternoon on the same day by her brother Tony at home."
Friends and family also took to Twitter to spread the word using the hashtag "#FindGemma":
Fellow ex-EastEnders actresses Brooke Kinsella and Martine McCutcheon have also helped publicise the case on Twitter.
Witnesses are urged to call the incident room on 020 8345 3985 or Crimestoppers anonymously on 0800 555 111.