A United Nations push to raise eight billion US dollars (£6.4 billion) for Syrian refugees has been backed by International Development Secretary Priti Patel.
The UN is seeking to get 4.63 billion US dollars (£3.7 billion) to help those displaced across the Middle East by the civil war, and 3.4 billion US dollars (£2.7 billion) to meet needs inside Syria.
Ms Patel said: "The UN's call-out to the international community today is the single biggest appeal it has ever made, highlighting that the conflict in Syria remains the world's biggest humanitarian crisis.
"The siege of east Aleppo at the end of last year reminded the world of the suffering and brutality that continues to be inflicted on the Syrian people after six years of unrelenting conflict.
"Schools and hospitals were hit and starvation used as a weapon of war. Hundreds were killed, tens of thousands more lost everything as they were forced to flee their homes.
"Sadly, the medieval siege tactics employed were not unique to Aleppo, we are seeing them used again and again across Syria.
"As many as 700,000 Syrians - nearly half of them children - remain under siege in 15 different parts of the country. Millions more have no regular access to the basic food, water and shelter they need to stay alive.
"Yet there is a very real risk that the barrel bombs, chlorine gas and indiscriminate violence that so shocked the world in Aleppo now becomes the new normal. We cannot become desensitised to such horrors.
"Britain has repeatedly set the pace in responding to this crisis and our commitment remains unwavering. UK aid ensured blankets, medical care, clean water and food reached those fleeing Aleppo.
"Across Syria, our support continues to mean the difference between life and death to hundreds of thousands more. We have pledged more than £2.3 billion to support those affected by the conflict, our largest ever response to a single humanitarian crisis."