Europe's sanctions regime against Syria was plunged into uncertainty after Britain, backed by France, forced a lifting of the EU arms embargo on what it identifies as the moderate opposition to President Bashar al-Assad.

Britain claimed victory in a long day of acrimonious negotiations, winning an easing of the arms embargo. The vast majority of EU states opposed the shift, but assented in order to preserve a semblance of unified policy.

A meeting of EU foreign ministers descended into recrimination with a vast majority against lifting the arms embargo, but William Hague, the foreign secretary, blocked a compromise deal. Austria, the biggest opponent of the British aim, reacted bitterly, stating that the EU negotiations had collapsed and that the Europe-wide sanctions regime would collapse at midnight on Friday.

Hague sounded satisfied, however, although others said 25 of 27 EU governments opposed the Anglo-French policy.

"EU nations agreed to bring the arms embargo on the Syrian opposition to an end. This was the outcome that the United Kingdom wanted. It was a difficult decision for some countries but it was necessary and right to reinforce international efforts to reach a diplomatic solution to the conflict in Syria," Hague said.

By contrast, the Austrian vice-chancellor and foreign minister, Michael Spindelegger, said the talks "have failed … I'm a little annoyed … It's regrettable that we have found no common position."

He added that France joined Britain in demanding a lifting of the arms embargo, but that the other 25 were opposed.

The Dutch said that only two EU countries were thinking of supplying arms to Syria, meaning the UK and France. There was also agreement that Britain would not begin to deliver arms to the Syrian opposition before August, in order to gauge what might happen at the internationally sponsored peace talks in Geneva mooted for next month, although there is no certainty whether they will take place.

The long day of negotiations between the EU's 27 foreign ministers saw Britain and France opposing plans to shelve a decision on arming the opposition until August, while Austria and the Czech Republic spearheaded the opposition to the Anglo-French push, with the Czechs supporting the Israeli line against sending arms to Syria and the Austrians alarmed at the impact on their UN peacekeeping mission in the Golan Heights between Syria and Israel.

Spindelegger said that Vienna would now have to reconsider its deployment on Golan. A withdrawal could see an Israeli rush to fill the UN vacuum, ratcheting up the tension in the region.

Laurent Fabius, the French foreign minister, said Paris supported a decision that would maintain an EU consensus, but would allow "the rebels to have the necessary arms and that the arms could be monitored".

The foreign secretary, William Hague, joined the French in arguing that supplying arms to "moderate" opposition forces would lead to less killing in Syria. Others argued the opposite, that arms supplies would only escalate the conflict.

Several countries – notably Austria, the Czech Republic, Finland, the Netherlands and Sweden – opposed the decision for fear that weapons might fall into the hands of Islamic extremist groups such as Jabhat al-Nusra. Germany has been trying to fashion a compromise.

Guido Westerwelle, the German foreign minister, said he would try to "build bridges", but consensus was elusive with participants delivering contradictory statements. Both Westerwelle and Hague had warned the EU could fail to agree a common position on the sanctions package, which was to expire automatically on Friday.

It appeared that Britain and France had received a green light to go ahead with supplying arms to the Syrian rebels. They have been pressing for a partial lifting of the arms embargo to the moderate sections of the Syrian opposition since last November. Hague has argued that lifting the arms embargo would complement, rather than contradict, a peace process since a militarily strengthened Syrian opposition can force the Syrian president, Assad, to the negotiating table.

Fabius returned early to Paris to meet John Kerry, the US secretary of state, and Sergei Lavrov, the Russian foreign minister, to try to organise Syrian peace talks in Geneva next month. No date has been set for the talks. It is not clear who will attend.

In Brussels, Turkey's foreign minister voiced strong support for the Anglo-French position. But last week in the US, Ankara was strongly rebuffed in its hawkish position against Assad by the White House.

Oxfam's head of arms control, Anna Macdonald, said: "Allowing the EU arms embargo to end could have devastating consequences. There are no easy answers when trying to stop the bloodshed in Syria, but sending more arms and ammunition clearly isn't one of them.

"Transferring more weapons to Syria can only exacerbate a hellish scenario for civilians. If the UK and France are to live up to their own commitments – including those set out in the new arms trade treaty – they simply must not send weapons to Syria."

The UK-French attempt to lift the arms embargo has not been made any easier by the continued lack of unity within the rebel movement. Talks failed on Sunday to end a factional dispute over proposals to dilute Qatar's influence on rebel forces, with Saudi Arabia angling to play a greater role now that Iranian-backed Hezbollah is openly fighting for Assad.

The dispute over how to respond to the civil war in Syria has exposed deep divisions in Europe. Senior European officials say much of the debate is "hypocritical" because some of the countries calling for a lifting of the embargo do not have the weapons to deliver or have no intention of taking part. They also point out that the White House and the State Department appear to be similarly split between hawks and doves.