LONDON — Britain said on Sunday it and other countries were "very reluctant" to arm rebels in Syria even as it warned that success on the battlefield by forces loyal to President Bashar al-Assad was undermining chances of a Geneva peace conference.

Britain and France worked together last month to lift a European Union embargo on arms shipments to Syrian rebels, giving them the flexibility to send weapons to forces who complain they are dramatically out-gunned.

But Foreign Secretary William Hague said on Sunday that no such decision had yet been taken and promised for the first time to give lawmakers a vote in parliament if and when it was.

"There would be a vote one way or the other," he told BBC TV, saying Britain and the world were faced with an agonizing foreign policy and ethical dilemma.

"People have understandable concerns about the idea of sending arms to anybody in Syria and we'd all be very reluctant to do that," he said.

"On the other hand, at the moment, people are being killed in huge numbers while the world denies them the right to defend themselves."

Hague's intervention comes as U.S.-Russian efforts to convene a peace conference in Geneva are faltering after the rebels lost control of the strategic border town of Qusair last week, weakening their negotiating hand.

One rebel commander has since been quoted as saying the opposition will boycott a peace conference unless it receives arms.

But Prime Minister David Cameron's government is split on the issue with some ministers fearing such a move could worsen the bloodshed and drag Britain into a protracted conflict.

Hague said he was gloomy about the prospect of a Geneva peace conference.

"The regime has gained ground. That makes the Geneva conference harder to bring about and to make a success. It makes it less likely that the regime will make enough concessions in such negotiations, and it makes it harder to get the opposition to come to the negotiations.

"They're not coming together in the next couple of weeks. I find that worrying and depressing," he added.

The United Nations estimates at least 80,000 people have died in the Syrian conflict.

U.N. humanitarian agencies launched a $5 billion appeal on Friday, the biggest in their history, to cope with the fallout from the fighting that has sent some 1.6 million refugees fleeing to neighboring countries.