In New York this week, addressing the UN General Assembly, David Cameron said of Syria: "The blood of these young children is a terrible stain on the reputation of the United Nations." This is too glib. The reputation that is being damaged is not that of the UN, but of the five permanent members of the Security Council: China, France, the US, Britain and Russia. They are the core of the realpolitik that has meant that the UN did not go the way of the League of Nations, even during the strains of the Cold War. It is the responsibility of these nations to forge realistic compromises and take account of their differing interests.

It has been my lot to spend many years negotiating with forces fighting each other in civil wars, predominantly in Southern Rhodesia and Bosnia Herzegovina. Both conflicts were complex in origin and bedevilled by intervention, from, respectively, South Africa and Serbia. The conflict in Syria leaves me with one overriding conclusion. Letting civil wars burn themselves out can have dangerous consequences. Consider Robert Mugabe's conduct in Zimbabwe, bringing in North Korea to train the Fifth Brigade to unleash genocidal violence against the Matabele. Or Bosnia today: in June 2011, Hillary Clinton and William Hague warned that for half a decade there had been a marked deterioration.

Syria is becoming ever more a Shia-Sunni religious conflict as the smaller groupings within are marginalised and leave the country.Ban Ki-moon, the UN Secretary General, in his speech to the General Assembly, urged the setting in motion of a Syrian-led transition as soon as possible. He had persuaded his predecessor, Kofi Annan, to take on the task of negotiator. When Annan stepped down, he could not hide his frustration that he had been given so little help by the Permanent Five.

The new UN negotiator since September 1, Lakhdar Brahimi, a former Algerian foreign minister, is superbly qualified for this challenge. He has signalled that the situation is bad and getting worse, and he cannot see any prospect of an early breakthrough.

The most worrying factor is the inevitable spillover to Iraq. There, the Shiite prime minister, Nuri al-Maliki, has moved closer to the Shiite fundamentalist regime in Iran since the withdrawal of the US military at the end of 2011. Al-Maliki fears that Sunni fundamentalists in Syria might replace the Assad regime and then support Sunni insurgent elements in Iraq. Flights from Iran now freely cross Iraqi air space, ferrying weapons and troops to support the Syrian dictatorship.

Meanwhile, Turkey is flying into Iraqi airspace to bomb Kurdish insurgents, who are raising the temperature in their age-old dispute. It is a grim picture and does not augur well for settling the oil dispute between the Kurdish regional government in Iraq and the central government in Baghdad.

The time has long since come for the US, UK and France to stop castigating the Russian Federation and China for their lack of co-operation over Syria in the Security Council. It is important to understand the strength of feeling among the Russian leaders that they were cheated over the UN Resolution - which they did not veto - allowing the establishment of a Nato-imposed no-fly zone over Libya. They believe Nato became an instrument of regime change, forcing out Gaddafi, contrary to the wording of the Resolution. As a consequence, they will veto any similar resolution over Syria.

I was one of the first to argue for a no-fly zone over Libya. Nato acted just in time to stop a massacre in Benghazi, and its military commanders had strong arguments for extending their mandate. Now, in the case of Syria, the arguments need to be rationally discussed, in particular with Russia. Military figures should give reassurance that such mission creep is not inevitable. Syria desperately needs both a Brahimi-led negotiated transitional arrangement, involving a ceasefire, and a way of dealing with violations of it. Realistically, Nato is the only organisation that the Security Council can charge with the responsibility of mounting a no-fly zone.

My suggestion is that the UN Secretary-General should ask the Nato Secretary-General to refer the question of how to sustain a ceasefire in Syria to the Nato-Russia Council. In that forum, which has never had its potential tested, it might be possible for military commanders as well as diplomats in Brussels to thrash out rules of engagement from the air with no boots on the ground in Syria.

It almost certainly would not involve, as in Libya, taking out with cruise missiles and aircraft all Syrian ground-to-air missiles, the safest way of proceeding. It would have to allow Nato planes to fire if any Syrian radar locked on to Nato aircraft. It should also involve Turkish military commanders in the discussions, which might help to defuse tension in the Nato-Russian Council. For even though Turkey, unlike Russia, is a vocal critic of Assad, the two countries have good working relations.

Without some new forum, the Security Council deadlock seems destined to continue, and peace in Syria will remain a distant dream.

Lord Owen served as British Foreign Secretary from 1977 to 1979, the youngest person in more than forty years to hold the post.