G8 foreign ministers meeting in London have said they are "appalled" by the rising death toll of more than 70,000 in the Syrian conflict and urged all countries to boost contribution to a UN aid appeal for the country.

But they have made no mention of supplying arms to the rebels as the opposition has demanded, saying only that there should be greater "humanitarian" assistance for those caught up in a conflict that is now in its third year.

In a statement issued by the ministers on Thursday after wrapping up two days of talks, they "expressed deep concerns about the increasing human tragedy of the conflict in Syria".

"They were appalled that more than 70,000 people have been killed in the conflict and that there are now more than a million Syrian refugees registered by the UNHCR in neighbouring countries, and more than two million internally displaced persons in Syria," they said.

"They called on all countries to join with them in maximising their contributions to the latest UN appeals and to provide them with direct support in order to help them face this challenging situation."

British Foreign Secretary William Hague, speaking after talks with his counterparts, admitted the world had done too little to try to resolve Syria's two-year-old conflict.

"The United Nations Security Council has not fulfilled its responsibilities because it is divided. That division continues. Have we solved that division at this meeting? No. We didn't expect to do so," Hague told reporters.

"The world has failed so far in its responsibilities and continues to do so."

Backing for Brahimi

The ministers reaffirmed their support for UN-Arab League envoy Lakhdar Brahimi and for finding a political transition in Syria, they said.

The statement also urged all sides in the conflict, which has now entered its third year, to respect human rights.

It said any use of chemical weapons "would demand a serious international response".

The G8 ministers called for "greater humanitarian assistance and for improved and safe access to the Syrian people by humanitarian agencies in coordination with all parties to the conflict".

John Kerry, US secretary of state, met Syrian opposition leaders on the sidelines of the talks on Wednesday to discuss their demands for sophisticated weapons to fight President Bashar al-Assad's forces.

But US officials said Kerry made "no promises", with Western nations concerned that any weapons supplied to Syrian rebels could fall into the hands of al-Qaeda-linked rebels.

A senior State Department official confirmed that, during a lunch hosted by Hague on Wednesday, the Syrian opposition leaders renewed appeals for lethal weapons but Kerry "didn't promise anything".

Hague, in a statement issued after the talks, said Britain was committed to finding a political solution to the crisis.

"We discussed what further assistance the UK could provide to save lives in Syria, and how we could work together to ensure this support was channelled most effectively," he said.

Before Thursday's morning session Guido Westerwelle, German foreign minister, reiterated that he is reluctant "when it comes to the topic of direct arms deliveries to Syria".

"To date I have seen no way to prevent these weapons getting into the wrong hands, namely those of radicals," he said.

"My concern is that weapons that are delivered to Syria will then get into the hands of jihadists and terrorists which then could be deployed against moderate democratic forces, and I fear that some jihadist or Islamist terrorists see Damascus as a stopover to Jerusalem at best."