Britain is to give an extra £5m to Syrian rebels fighting Bashar al-Assad's regime, helping to fund additional communications equipment and medical supplies, but not weapons.
William Hague said the financial assistance was made in light of the "absence of diplomatic progress" and would help protect civilians from "some of the worst of the violence".
"It's well recognised that the situation in Syria is an affront to the conscience of humanity," the foreign secretary said on Friday.
Hague said the UK would not provide any weapons to the Free Syrian Army
"The people of Syria cannot wait indefinitely. People are dying and are trapped without food and shelter."
He said the funding would "help protect unarmed opposition groups, human rights activists, and civilians from some of the worst of the violence.
"This is assistance that will help save lives, not abandon all Syrians to the mercy of the regime. It will help people caught up in a terrible conflict."
Earlier, in a letter to The Times published on Friday, the foreign secretary said the government was actively pursuing a life after Assad, and sought to build relationships with political groups opposing president Assad.
But Hague denied the move was taking sides in a civil war.
"The risk of total disorder and a power vacuum is so great that we must build relationships now with those who may govern Syria in the future.
"If we do not work with those Syrians who want to see a democratic and open country, we leave a void to be exploited by al-Qaeda and others with extremist agendas who wish to hijack the conflict," he wrote.
He said medical and communications equipment, including cameras, video recorders, forensic equipment, paramedic kits, water purification equipment and portable power generators would be funded, alongside assistance to injured and displaced people.
"We have quadrupled British aid for Syrian refugees and are helping to feed more than 80,000 Syrians every month, including in Aleppo and Idlib. We are supplying medical stocks to field hospitals giving emergency medical care, blankets and mattresses in places such as Homs."
But he also warned Syrian rebels "that they must observe human rights standards, whatever horrors are perpetrated by the regime".
Earlier this month Human Rights Watch warned the Free Syrian Army they could be responsible for war crimes after video purporting to show the execution of pro-Assad forces emerged.
The organisation's Middle East deputy director Nadim Houry sparked controversy with his comments calling for rebels to be held to account.
"Intentionally killing anyone, even a shabiha [a member of Assad's armed gangs], once he is outside of combat is a war crime, regardless of how horrible the person may have been," he said.
A foreign office spokesman said: "As the Foreign Secretary says, we need to work with the Syrian opposition to ensure they prepare for the inevitable day of Assad's fall, including representatives of the Free Syria Army.
"We are therefore meeting political elements of the Free Syria Army."