Women and girls risk becoming the "forgotten victims" of the Syrian crisis, International Development Secretary Justine Greening has said, as the number of refugees fleeing the country reached one million.
Thousands of families are now crossing the nation's borders each day to escape the increasingly violent conflict, with neighbouring countries severely impacted by the conflict.
Around two-thirds of those caught up in the exodus are women and children, the majority of which are under the age of 11. Many arrive traumatised and without possessions.
International donors are being called upon to deliver the humanitarian help they pledged. Without vital support Greening said, women and children could find themselves victims of long-term displacement and financial hardship. This could expose them to exploitation and abuse.
"One million refugees is a terrible landmark and the most vulnerable groups are inevitably those who find themselves at greatest risk," she said.
"Syria's neighbours cannot deal with this alone and all donors must rapidly deliver on the promises they made in Kuwait."
She spoke as the UN's refugee agency said more than 400,000 Syrians have left their homes since January, with the number registered as refugees or receiving assistance topping one million.
Syria is now "spiralling towards full-scale disaster", said the UN High Commissioner for Refugees Antonio Guterres.
Most refugees have escaped to Lebanon, Jordan, Turkey, Iraq and Egypt, with Syrians increasingly fleeing to North Africa and Europe.
Ms Greening called for measures to address violence against women and girls to be systematically factored into all humanitarian work in the region.
Further efforts should be focused on protection and support for the elderly and chronically ill, she said.
At least four million people are believed to be in desperate need within Syria, alongside the one million refugees who are now dependent on the generosity of host countries.
Lebanon's population has increased by as much as 10% since the crisis struck, nearly two years ago, while Jordan's energy, water, health and education services are being "strained to the limit" according to Guterres.
Turkey has spent around £4 million setting up 17 refugee camps, with more under construction, and Iraq has taken in more than one hundred thousand Syrians in the past year.
"These countries should not only be recognised for their unstinting commitment to keeping their borders open for Syrian refugees, they should be massively supported as well," Mr Guterres said.
In December, the UN estimated some 1.1 million Syrians would arrive in neighbouring countries by the end of June.
The UNHCR refugee agency is now adjusting this plan - which is only 25% funded - in light of the new figures.
David Bull, executive director of children's charity Unicef in the UK, said the arrival of the millionth refugee across the Syrian border was a "grim milestone".
He said: "Of those million refugees, at least half are children; many of whom have suffered tragic loss and witnessed horrific violence.
"In Syria itself, a further two million children are in urgent need of humanitarian assistance.
"It is wrong that even one child in Syria or outside its borders is living in fear or without the basic help needed to survive and Unicef is working day and night to reach children affected and provide vital help."
The charity is assisting young refugees in Syria, Jordan, Lebanon, Turkey, Iraq and Egypt but conceded it was "desperately short of funds" and could be forced to cut some of its relief work.
"Unless an 80% funding gap is bridged, Unicef will be forced to scale back on our life saving interventions," Mr Bull said.
He added: "As of next month, we might not have enough funds to provide children and their families in Syria with clean drinking water. Without this, many thousands of children could be exposed to serious and potentially life-threatening waterborne diseases."