THE announcement that Britain is stepping up its support to Syrian rebels marks a new stage in the UK`s engagement with the opposition forces. Tragically, this month also marks the second anniversary of the start of the brutal conflict, with the death toll now estimated at over 70,000, and one million made refugees.

While primary responsibility for this crisis rests with President Assad and his brutish regime, this humanitarian catastrophe also represents the abject failure of the international community to act decisively and collectively.

In the face of this failure, it is understandable that the UK, alongside other EU states, is seeking to do more to exert influence over a deteriorating situation.

But a policy born of frustration is less likely to deliver than one based on clear thinking and strategic insight. For the international community this represents a diplomatic, not military, failure. The pressing task remains not to arm the rebels but to unify them.

To be successful, any assistance to the Syrian National Council must have clearly defined parameters. The country today is awash with arms and it is impossible to guarantee the end use of weapons given the lack of clarity about the identity, intent and tactics of some of the rebel forces. Reports of the presence of AlQaeda linked militants and the al-Nusra Front within Syria should cause the international community to reflect carefully before repeating past mistakes.

Only this week the UN suggested that human rights violations are now taking place on both sides of the conflict and that it is turning into a `destructive stalemate`. Increasing technical and nonlethal support for the opposition must not be simply a ramp towards arming the rebels. Indeed it is perfectly possible that if Europe were to decide to arm the rebel forces, the Russians would simply increase their supply of arms to the Assad regime.

News that the UK will fund training for the rebel forces has caused concern on all sides in parliament. Subsequent revelations in the Guardian that British and American forces are already involved in training some Syrian opposition forces in Jordan raises questions as to the real direction of policy. So while the government has our support for its actions to provide humanitarian assistance to Syria, it is far from clear if taking steps that may intensify this conflict will do anything to reduce the appalling level of suffering. The choice is not between increasing military support and doing nothing at all. Eleven separate rounds of sanctions against Syria have already been agreed, so the issue at present is not necessarily new sanctions, buteffective enforcement. Better enforcement, particularly from countries like Lebanon within the Arab League, could help choke off the financial support that sustains Assad.

Although he will not say so publicly, even President Putin must now doubt the long-term durability of the Assad regime. For all parties, a real question now is: what comes after Assad falls? It is in no one`s interest neither the west, nor Russia to see a `catastrophic victory` in Syria whereby Assad goes, but the power vacuum leaves a failed state in the heart of the Levant. A credible political transition is needed in order to avoid this. The gap between what Russia and the west want for Syria is not unbridgeable. This week the UN`s special envoy, Lakhdar Brahimi, and secretary general, Ban Ki-moon, have again called for a renewed diplomatic initiative, led by the UN, to bring all the warring parties to the table.

Today, as (UK foreign secretary) William Hague meets the Russian foreign minister, Sergei Lavrov, in London, his primary task must be securing Russian support for this initiative, not further widening the divide.

By arrangement with the Guardian Note: Douglas Alexander is the UK`s shadow foreign secretary