Britain's outgoing head of the armed forces has warned that attempts to impose a no-fly zone over Syria would be unsuccessful without establishing ground control, in an interview published in Thursday's Daily Telegraph.
Britain is at the forefront of international efforts to topple the regime of President Bashar al-Assad, and has promised to supply rebels with equipment to protect them against chemical weapons attacks.
But in his interview with the Telegraph, General David Richards said: "If you wanted to have the material impact on the Syrian regime's calculations that some people seek, a no-fly zone per se is insufficient.
"You have to be able, as we did successfully in Libya, to hit ground targets. You have to take out their air defences."
Richards stressed that a "ground control zone" would need to be established and that tanks and armoured personnel carriers would have to be "taken out".
"If you want to have the material effect that people seek you have to be able to hit ground targets and so you would be going to war if that is what you want to do," he added.
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A lack of international consensus and the splintered nature of rebel forces made it difficult to forge a military solution, the 61-year-old general added.
Richards retires on Thursday after a military career spanning more than 40 years.
British Foreign Secretary William Hague has promised lawmakers that the government would seek parliament's consent before deciding to arm the rebels.
There has been concern that the weapons could fall into the hands of radical Islamist opposition groups.
Prime Minister David Cameron said last month, however, that the government reserved the right to intervene in Syria if it felt Britain's national interests were under threat.
More than 100,000 people have been killed since the uprising against Assad erupted in March 2011, according to the Syrian Observatory for Human Rights.