We must tackle the source of the Isil threat But when it comes to tackling the root cause of the problem - namely the independent fiefdom that Isil militants have created in northern Syria - the Government's response is less convincing. While Isil's reach extends well beyond Syria's borders into Iraq, the intelligence assessment is that most of its terrorist activities targeted at the West originate from Syria. This is where the majority of the beheadings are thought to have taken place, and where many of the plots are hatched. The Government therefore finds itself in an uncomfortable position - because, for the moment at least, Britain's military contribution to the international effort to confront Isil is primarily centred on Iraq. RAF Tornado fighters and Reaper drones are flying daily missions in support of the US-led air campaign. On the ground, British military trainers and special forces are supporting pro-Western militias, such as the Kurds" Peshmerga fighters, in an attempt to reverse Isil's territorial gains. In Syria, by contrast, the Government's response is more constrained - not least because of the political fall-out from last year's disastrous Commons vote, when David Cameron's proposal to launch air strikes against president Bashar al-Assad was defeated. Consequently, Britain's military involvement in Syria is confined to providing intelligence on potential bombing targets, as well as funding training for moderate opposition fighters fighting Assad and Isil. Neither of these options inspires confidence. Providing coalition warplanes with intelligence so that they can bomb Isil targets on our behalf smacks of moral cowardice; meanwhile, proposals to train a new army of moderate Syrian rebels at camps in Jordan have foundered because of the paucity of recruits. Britain is not the only country struggling to decide how best to deal with Isil in Syria. The departure of Chuck Hagel, the US defence secretary, this week is said to have been prompted by his differences of opinion with the White House on the issue. And Mr Cameron is well aware of the difficulties he faces in trying to rally political support for escalating Britain's military involvement, especially as Ed Miliband has signalled he is not prepared to support such a move. But the longer the Syrian conflict continues - it has already claimed an estimated 200,000 lives - and the more Isil grows in strength, the more untenable the Government's position will become. Domestic political differences may limit Mr Cameron's options, but they do not mean he should not attempt to make the argument for further intervention. There is, of course, another option he could consider, which is to revive diplomatic efforts to end the bloodshed, thereby allowing everyone to focus on destroying Isil. Islamist militancy is a threat to Russia, one of the Assad regime's main backers, as well as the West - but the belief that Moscow is totally opposed to doing a deal over Syria has been the major obstacle to ending the fighting. Yet only last weekend, Philip Hammond, the Foreign Secretary, was involved in negotiations with the Russians to resolve the crisis over Iran's nuclear programme. Which raises the question: if we can work with the Russians on Iran, then why not on Syria?