Theresa May has described the terrorist attack in Tunisia in which at least 18 Britons are confirmed to have been killed as a "despicable act of cruelty", as she held a press conference in the country.
On Monday afternoon Downing Street said all Britons injured in the Sousse terror attack will be returned to the UK within 24 hours.
A total of 38 people perished after a gunman opened fire on a beach in the resort on Friday. Up to 30 Britons are feared to have been killed.
David Cameron said today that Britain must become "intolerant" of extremist Islam in order to protect "the very things we stand for".
The prime minister today chaired the Cobra emergency committee where the need for British authorities to be given support in Sousse to "swiftly" identify those killed was raised.
The spokesman confirmed an RAF C-17 aircraft was sent out the resort this morning to bring back four Britons injured, and a number have also been brought home privately.
May and Foreign Office minister Tobias Ellwood have travelled to the country to pay their respects and take part in talks with the Tunisian government on addressing the extremist threat.
Earlier today, the home secretary visited the scene of the massacre. She laid flowers and observed a period of silence in the Sousse resort.
Speaking at a press conference alongside the Tunisian interior minister, May said the attack was "a despicable act of cruelty". She added: "How could a place of such beauty, of relaxation and happiness be turned into such a scene of brutally and destruction".
"I have heard of the stories the horror stories of people who went though this and our thoughts are with the victims and their families. I have also heard stories of great bravery as well."
"I would like to thank the Tunisian authorities, the Tunisian government and the staff here at the hotel for all they have done to help and support he victims.
May said as the country's first democratically elected president, Beji Caid Essebsi was a "symbol of what is possible" in North Africa.
The home secretary said: "We are very clear that the terrorists will not win. We will be united in working tighter in working together to defeat them."
She said the UK and Tunisia would unite to "defeat those who would do us harm". and "to defeat those who would undermine our freedom and democracy and to ensure the terrorists do not win".
Writing in The Daily Telegraph, the Prime Minister said that the United Kingdom must "be stronger at standing up for our values" as the death toll from Friday's massacre continues to rise.
Cameron said that Britain is "united in shock and in grief". He suggested that the government is preparing to take a firmer stance in order to "root out this poison" in the UK as well as abroad by supporting foreign governments.
Cameron said it was important to deal with the terrorist organisation "at its source" in places such as Syria, Iraq and Libya where IS was "peddling and plotting its death cult".
He continued: "When the gunman attacked innocent people spending time with their families on the beach, he was attacking the very things we stand for.
"We must be stronger at standing up for our values – of peace, democracy, tolerance, freedom. We must be more intolerant of intolerance – rejecting anyone whose views condone the Islamist extremist narrative and create the conditions for it to flourish.
"We must strengthen our institutions that put our values into practice: our democracy, our rule of law, the rights of minorities, our free media, our law enforcements – all the things the terrorists hate."
On Saturday evening, Tunisians marched through Sousse in protest at the terrorist atrocity. Many carried the British flag.