A Palestinian refugee, his partner and their teenage daughter who died after getting into difficulty in the sea off Shoreham have been named by police.

Hassan El-Khawas, 55, his partner Zeina Alayn, 37, and their 14-year-old daughter Sara El-Khawas are thought to have gone into the water to swim alongside a young female family member near Shoreham Fort in Shoreham-by-Sea, West Sussex, on Tuesday afternoon.

Police, paramedics, coastguard crews and a lifeboat went to the scene where four people were pulled from the water.

Three were pronounced dead on Tuesday, while the young girl remains in hospital in a critical condition.

It is understood the family travelled from their home in London to visit Shoreham, officers said.

Sussex Police said its investigation remains open, but after a review of CCTV footage and initial witness accounts, it is currently thought the deaths were a tragic accident, with no third-party involvement.

Sources have said there is currently no evidence to suggest a fishing net was involved.

Earlier on Wednesday, the Palestinian embassy said Mr El-Khawas was a Palestinian refugee from the Rashidieh Camp in Lebanon but did not give details about the other family members.

Rashidieh Camp is on the Mediterranean coast in southern Lebanon and is one of the most populous Palestinian refugee camps in the country.

The older part of the camp was built by the French government in 1936 to accommodate Armenian refugees who fled to Lebanon, while the newer part was built by United Nations Relief and Works Agency for Palestine Refugees in the Near East in 1963 for Palestine refugees, according to the agency.

In a statement on Facebook, the Palestinian embassy said it was “closely monitoring the incident”.

It added: “As the embassy extends its deepest condolences and sympathy to the victims’ family, their loved ones, and members of the Palestinian community in the United Kingdom in this painful affliction, it wishes the injured girl a speedy recovery.”

In a statement, Adnan Hmidan, chairman of the Palestinian Forum in Britain, paid tribute to the family, although his spelling of their name differed from that used by Sussex Police.

He said: “The Palestinian, Arab and wider community in Britain, along with the many friends and supporters of our community, have been deeply shocked and saddened by the tragic incident involving the Khawwas family during a day trip off the coast of Sussex yesterday.

“Our thoughts and prayers are with the entire family, particularly the children, who are facing an unimaginable loss. We ask everyone to respect their privacy and dignity at this painful time.

“We especially appeal to members of the media not to approach or disturb the family or the children while they are grieving and trying to come to terms with this devastating tragedy.

“The relevant authorities are carrying out the necessary procedures and investigations, and we ask that the family be given the space and time they need while those processes take place.

“Our community stands united with the Khawwas family. We will continue to support them in every way we can and to ensure that they know they are not alone.”

Prime Minister Andy Burnham warned of the dangers of open water swimming after the incident, which he described as “a terrible family tragedy”.

He said: “The thing I can say today – and there is still, I think, a further heatwave to come in this summer period – it is just to remind people about the dangers of open water swimming.

“The coldness, even when it feels hot outside, it can shock people and that can cause the difficulties. So people just need to remember that at all times.

“I do need to praise the emergency services who I know were on scene very quickly yesterday. They’ve had a busy summer but they were there and we thank them.”

The family are believed to have entered the water near to the 19th century Shoreham Fort on the harbour.

Video footage showed a number of emergency services searching an area of water near to an arm of the harbour where the River Adur meets the sea.

Chief Superintendent James Collis said: “The events of Tuesday afternoon are a heartbreaking tragedy which has devastated a family and their friends and had a profound impact on the Shoreham community.

“The thoughts of all at Sussex Police remain with the family’s loved ones as we work with our partners, including HM Coroner, to understand exactly how this incident occurred.

“The emergency response was significant, and I would like to thank all of the first responders for their determined attempts to save all four people, as well as the wider public for their patience during the incident.

“We will release further updates as soon as we are able, but we ask the family are given the privacy they deserve at this incredibly difficult time.”

The force said it will prepare a file for the coroner ahead of any inquest.

Nearby residents told of their shock at the tragedy and their concerns for the girl fighting for her life.

Joss Loader, who lives nearby and represents Shoreham Beach Residents’ Association on Adur District Council, said: “There’s just a really strong sense of shock, obviously people are really concerned for the young girl.

“It’s school holidays and we have had a wonderful summer so the beaches have been packed with families.

“The weather was quite calm, not as hot as recent days but it was a perfectly normal day.

“People swim from those beaches even in the winter, generally it is considered as safe as the sea can be. You wouldn’t be swimming there and think you were taking a risk.”

But others warned that swimming at Shoreham can be dangerous.

Anna Peacock, 81, who lives near Kingston Beach across the water from Shoreham Fort, said: “People come down to swim, particularly in the summertime, and I don’t think they realise there’s a riptide along here.

“It’s very inviting to come to the sea, but the tide could carry you out in seconds, and I don’t think people have realised that.”

Robina Baine, also an Adur councillor who represents the Southwick Green ward where the RNLI lifeboat station is, said: “These events are absolutely tragic and our thoughts are with the family and friends that have lost their loved ones.

“I have been here for 46 years and this is the most tragic incident there has been.”