The UN Refugee Agency said over one million Syrians who have fled the violence to neighbouring countries are children:
The UN Refugee Agency (UNHCR) has released a breakdown of the number of refugees that have fled the violence in Syria to neighbouring countries.
David Cameron said Britain has spent over £300 million and "saved tens of thousands of lives" in Syria.
The Prime Minister said: "I've been to Jordan and seen one of the refugee camps myself and I know how much money and how much effort is going in.
"Britain, as ever, is a world leader at helping those who need help, and the people of Syria are right up at the front of that right now."
1 year ago: 230,000 Syrian refugees. Today: 2,000,000. 1/2 children. If we don't end the conflict, think what the figure could be next year
UK is 2nd largest bilateral donor to Syrian refugees, helping around 900,000 people, but there is still a huge aid shortfall
ITV News' correspondent Martin Geissler has been reporting from the world's second largest refugee camp in Jordan.
One of two million refugees who have fled Syria said he was angry that the world had not done more to stop President Bashar al-Assad from using chemical weapons: "What is the matter with the world? Are they sleeping? Are they drunk? Are they on drugs?"
The number of refugees fleeing Syria for camps in Iraq and Jordan is "astonishing", children's charity UNICEF has said to Daybreak.
Jon Sparkes, who recently returned from the Iraq camp, described problems with fresh water, sanitation and the legacy of "a generation" of displaced children.
The UNHCR has issued a fresh warning about the Syria refugee crisis as their number passes the two million mark. There are now more displaced Syrians in the world than any other nationality.
- 2 million refugees have crossed the border
- 4.25 million have been displaced within Syria
- 700,000 have fled to Lebanon, where they account for 1 in every seven people
- Most of the others are in Jordan, Turkey or Iraq
- Only 3 percent have fled further afield
Oxfam has said it is "appalled" that the number of Syrian refugees has reached two million, adding that the humanitarian response is "stretched to the limit".
– Claire Seaward, Syria Response Campaign Manager, oxfam
Enough is enough. A generation of Syrians is paying too high a price in this conflict. They have been seriously let down by the international community, which has failed to prioritise a political solution to the conflict.
That must change. World leaders - especially President Obama and President Putin - must ensure the long-promised peace talks take place as soon as possible.
More than two million refugees have fled over borders to escape the fighting in Syria, according to new figures from the UN's refugee agency.
The vast majority - around 1.8 million - have left in the last year of the 30-month conflict, suggesting that the flow is increasing.
UNHCR also estimates that the number of people displaced within Syria's borders has swelled to 4.25 million.