Police and security services in Sri Lanka are continuing to investigate the Easter massacre which killed nearly 300 people including at least five Britons.

A series of blasts, most thought to be the work of suicide bombers, ripped through churches and luxury hotels on Easter Sunday.

The bombings are being treated as a terrorist attack by religious extremists and police have arrested 13 but there was no immediate claim of responsibility.

Srl Lanka Church BlastsA Sri Lankan Police officer inspects a blast spot at the Shangri-La hotel in Colombo (Chamila Karunarathne/AP)

Foreign Secretary Jeremy Hunt said there was “lots of speculation at the moment but there is no hard knowledge” about the perpetrators of the atrocity and “we obviously need to wait for the police in Sri Lanka to do their work”.

He said the UK would offer Sri Lanka support in the days to come.

“If there is any help that the UK can give, we would want to give it,” he said.

READ MORE: Mother and son among Britons feared dead

One line of inquiry will be asking what intelligence services knew about the attack, with Minister for Telecommunications Harin Fernando tweeting: “Some intelligence officers were aware of this incidence.

“Therefore there was a delay in action. What my father heard was also from an intelligence officer. Serious action need to be taken as to why this warning was ignored.”

In Colombo, St Anthony’s Shrine and the Cinnamon Grand, Shangri-La and Kingsbury hotels were targeted in the first wave of explosions shortly before 9am local time as worshippers attended morning services and tourists enjoyed their breakfasts.

Among the Britons feared dead are Anita Nicholson, 42, and her 11-year-old son Alex.

They were reported to have been dining in the Shangri-La when the bomber struck.

According to her LinkedIn profile, Mrs Nicholson was based in Singapore as managing counsel at the mining and metals company Anglo American.

Britons caught up in the carnage in Colombo described the horrific scenes they witnessed.

Following the blast at the Cinnamon Grand, NHS doctor Julian Emmanuel, from Surrey, told The Sun: “I’ve never seen such utter devastation.”

He added: “My children and wife are traumatised by what they saw today.

“We will never forget this.

“We will always remember Easter Sunday for this reason now.”

READ MORE: Five British citizens among those killed in Sri Lanka explosions

Kieran Arasaratnam, a professor at Imperial College London Business School, was staying at the Shangri-La.

“Everyone just started to panic, it was total chaos,” he told the BBC. “I looked to the room on the right and there’s blood everywhere.

“Everyone was running and a lot of people just don’t know what was going on. People had blood on their shirt and there was someone carrying a girl to the ambulance. The walls and the floor were covered in blood.”

Hampstead and Kilburn MP Tulip Siddiq said she had lost a relative in the attacks.

She posted on Twitter: “It’s all so devastating. Hope everyone is keeping safe. Solidarity with the people of Sri Lanka.”

Prime Minister Theresa May said the Easter Sunday massacre was “truly appalling”, and “no-one should ever have to practise their faith in fear”.Three Britons and two holding joint US and British nationalities were killed, Sri Lankan authorities said.

Mr Hunt said the death toll of five Britons killed in the attack was “the latest figure that I have heard”.

“But obviously our High Commissioner is working on this with his team in the embassy in Colombo, working around the clock, and we are trying to gather as much information as we can about this,” he said.

He said the terrorist attacks were “absolutely devastating and despicable” and “for this to happen on Easter Day is something that will shake people around the world, of all faiths and none, to the core”.

At around the same time as the blasts in Colombo, explosions were also reported at St Sebastian’s Church in Negombo and at Zion Church in the eastern town of Batticaloa.

A few hours later, two more blasts occurred just outside Colombo, one of them at a guesthouse, where two people were killed, the other near an overpass.

Three police officers were killed during a search at a suspected safe house on the outskirts of Colombo when its occupants apparently detonated explosives to prevent arrest.

Sri Lanka bombings(PA Graphics)

The authorities said at least 290 were killed and more than 500 injured in the attacks.

A curfew was imposed by the authorities on Sunday night and social media use was also restricted by the authorities, which claimed the move was to prevent the spread of false information.

Sri Lanka Church BlastsFirefighters near St Anthony’s Shrine after a blast in Colombo, Sri Lanka (Eranga Jayawardena/AP)

Labour leader Jeremy Corbyn called for “unity, love and respect” to combat hatred.

He said: “I’m appalled by the horrific attacks in Sri Lanka, on Easter Sunday, the most important day in the Christian calendar.”

Archbishop of Canterbury Justin Welby said: “On this holy day, let us stand with the people of Sri Lanka in prayer, condolence and solidarity as we reject all violence, all hatred and all division.”

Sri Lanka’s prime minister Ranil Wickremesinghe condemned “the cowardly attacks on our people”.

Sri Lanka Church BlastsThe blood-spattered wall and statute of Jesus Christ inside St Sebastian’s Church, Negombo (AP Photo)

Nisanga Mayadunne, who studied at the University of London according to her Facebook profile, and her mother Shantha – a TV chef – were also reported to be among the dead.

Nisanga posted a photo of her family eating breakfast in the Shangri-La on Easter Sunday.

Britons in Sri Lanka who need help were urged to call the High Commission in Colombo on +94 11 5390639, while people in the UK worried about friends or family should call the Foreign Office on 020 7008 1500.