Britain, apparently backed by a handful of European Union allies, is fighting to lift an EU arms embargo barring the supply of weapons to the Syrian rebel coalition battling President Bashar al-Assad.
As EU foreign ministers arrived for a daylong meeting on the issue Monday, the internal row remained unresolved despite weeks of talks that diplomats from member states describe as both "difficult" and "divisive".
"I don't think there is at this point a common position," said the Cypriot minister Erato Kozakou-Markoullis on arrival. "It's a very serious, a very difficult issue."
But time is running out.
The EU's wide-ranging sanctions against Syria, including the arms ban but also targeting scores of Assad cronies and regime-friendly firms, as well as oil, trade and finance, expire at the end of the month and a deal to renew the package requires unanimity.
Britain and France had seen the March 1 deadline as an opportunity to respond to requests for weaponry by the opposition.
But France appears to have cooled, leaving Britain facing opposition from Germany, Sweden and even the EU's foreign affairs chief Catherine Ashton, a British baroness who represents London on the European Commission.
"Delivering arms might bring about a new military balance on the ground," said an internal paper on the matter drafted for the member states by Ashton's service.
"But it could also fuel further militarisation of the conflict, increase risks of dissemination among extremist groups and of arms proliferation in a post-Assad Syria," said the paper, which was obtained by AFP.
Among options on the table are restricting the embargo to the Syrian government, exempting members of the opposition Syrian National Coalition from the arms ban, or amending the embargo to allow some weapons to be delivered with a view to increasing the protection of civilian populations.
Luxembbourg's minister Jean Asselborn, a strong voice on the European diplomatic scene, warned on arrival that caution was key.
"There is no lack of weapons in Syria, rather the contrary. There are a lot of things lacking in Syria, but not arms," he said. "More arms will mean more deaths."
EU diplomats are concerned too over the timing of a lift of the arms embargo.
"There is a real question here," said a senior EU diplomat speaking on condition of anonymity. "But is this the right moment given the current efforts to push a political settlement?"
UN peace envoy Lakhdar Brahimi was supposed to attend Monday's talks with the EU ministers but had to pull out as efforts mount to make good an offer from opposition leader Ahmed Moaz al-Khatib to negotiate with some regime figures.
"In today's political context, would this be an appropriate measure?" added the diplomat.
Just over a week ago, French President Francois Hollande ruled out lifting the arms embargo for the time being, saying this could only happen "if we're sure there are no further possibilities of political dialogue."
And in Mali, France is facing a reality check "with its troops fighting rebels armed with western weapons from Libya," said an EU official.
US President Barack Obama last year refused to arm Syria's rebels on the same grounds.