Prime Minister Theresa May has ordered a full public inquiry into the fire that engulfed a west London block of flats, killing at least 17 people.
The prime minister spoke to fire commissioner Dany Cotton as she surveyed the damage.
That figure is expected to rise, as fire chiefs do not expect to find any more survivors in the burnt-out Grenfell Tower in North Kensington.
The PM said people "deserve answers" as to why the fire spread so rapidly.
The first victim has been named by the Syria Solidarity Campaign as Syrian refugee Mohammed Alhajali, 23.
Six victims of the blaze have been provisionally identified, Metropolitan Police Commander Stuart Cundy said, but "there is a risk that sadly we may not be able to identify everybody".
Asked about the number of dead, Cdr Cundy said: "I hope it is not triple figures, but I can't be drawn on the numbers."
Fled war in Syria
In a statement, the Syria Solidarity Campaign said Mr Alhajali, a civil engineering student, had been in a flat on the 14th floor when the fire broke out, and had spent two hours on the phone to a friend in Syria.
He had been trying to get through to his family while he was waiting to be rescued.
The group said: "Mohammed bid his friend goodbye, saying that the fire had reached him.
He asked his friend to pass on the message to his family...
"Mohammed undertook a dangerous journey to flee war and death in Syria, only to meet it here in the UK, in his own home.
"Mohammed came to this country for safety and the UK failed to protect him."
His older brother, Omar, told the BBC he had lost Mohammed on the way out of the building.
Earlier, Mrs May made a private visit to the scene, where she spoke to Fire Commissioner Dany Cotton and members of the emergency services.
She said: "[They] told me that the way this fire had spread and took hold of the building was rapid, it was ferocious, it was unexpected.
"So it is right that, in addition to the immediate fire report that will be produced and any potential police investigation, that we do have a full public inquiry to get to the bottom of this."
Number 10 confirmed the public inquiry will be judge-led. Sources say the government hopes to announce the name of the judge "soon", the BBC's assistant political editor Norman Smith said.
London Mayor Sadiq Khan heckled at tower.
London Mayor Sadiq Khan said one of the issues the inquiry would consider was whether the tower block had been refurbished in a safe way.
Labour leader Jeremy Corbyn also visited the site, meeting residents affected by the fire. He told community leaders "the truth has to come out".
The Labour MP Harriet Harman criticised Mrs May for not meeting residents, writing on Twitter: "She should have been prepared to listen to them."
BBC political editor Laura Kuenssberg said Mrs May's team believed the decision not to visit residents was made for the right reasons.
"They didn't want to get in the way, they wanted to allow the emergency effort to carry on unimpeded and, frankly, it is just not her style to have TV cameras trailing her every move," she said.
But she said the decision could "prove to be a miscalculation" because events like this "can require real displays of empathy".
(BBC)