David Miliband is president and chief executive of International Rescue Committee. He was Britain’s foreign secretary from 2007 to 2010.

It is a rare peace conference that brings immediate peace. But few have sparked such little optimism as the one planned for Wednesday in Montreux, Switzerland, to discuss Syria. As Laurent Fabius, the French foreign minister, has said, there is “a great deal of doubt” about whether progress can be made.

If peace is beyond reach, then the conference must, at a bare minimum, restore basic humanity to the conduct of war. This means addressing the desperate situation of Syrian civilians trapped by the fighting without food, health care, education or hope.

The problem is often described as one of access for humanitarian agencies. But that is like saying that someone who is being strangled is suffering from lack of access to air. The issue is bigger: The Syrian people are facing a blockade. They are under siege.

More than 9 million people have been displaced from their homes. A third of the country’s housing has been damaged or destroyed. Public services have been shattered. As of last month, nearly 40 percent of Syrian hospitals had been obliterated and 20 percent had been severely damaged. Almost 2 million children have been forced out of school in the past year.

The United Nations has the best estimates of acute need. A quarter of a million civilians are completely cut off, it reports, in besieged areas in Homs, Aleppo and greater Damascus. By U.N. estimates, 2.5 million people are in “hard-to-reach” areas such as al-Hasakah.

It’s not hard to understand why people are hard to reach. Reports emerge daily about how government forces are using siege as a weapon; rebel groups are fighting one another; civilians are caught in the middle. In fact, the very notion of a civilian — a noncombatant — has been lost, as snipers shoot women, doctors are targeted and suburbs are shelled.

The International Rescue Committee has helped close to a million Syrians gain access to medical care during the conflict. But people are burning clothes to stay warm. Clerics issue edicts about eating cats and dogs. And polio has broken out.

These issues must be addressed in Montreux — with practical plans for implementation and accountability.

First, adherence to international humanitarian law, which governs armed conflict, is a requirement, not an option, for both the Syrian government and rebels. The targeting of civilians, medical facilities and aid workers is illegal and needs to be challenged by supporters of both sides.

Second, the strong Oct. 2 presidential statement from the U.N. Security Council details the responsibility of all parties to allow the flow of aid and medical help. But that duty is not being honored — making a mockery of both the United Nations and its member states.

All permanent members of the Security Council, including Russia and China, supported that U.N. statement. If it is being ignored, they should be challenged to support a binding U.N. resolution with the same wording.

Third, special provision is needed to reach besieged communities. Parties to the conflict should appoint delegates empowered to negotiate the passage of aid and civilians across lines of conflict. From Afghanistan to Sudan, there is experience in negotiating and delivering humanitarian aid during civil wars. The United Nations has a high-level group, made up of member states, that works under the auspices of its Office for Coordination of Humanitarian Affairs; ensuring that hungry and frightened people receive relief should be its immediate focus.

Fourth, the fate of Aleppo needs to be the test of progress. Aleppo is Syria’s most populous city, with 2 million people crammed in. It is now a divided city and therefore home to precisely the conflict lines that test the humanity of both sides. Aleppo is to Syria what Sarajevo was to Bosnia. If Syria is ever to recover its tranquillity and beauty, this city must be saved from descending into hell.

If all this does not happen, the price will be severe. It will be paid by the Syrian people in the form of rampant disease, death and destruction. It will be paid in the region by the further spread of refugees into countries decreasingly able to cope. It will be paid by the wider world in the growth of toxic radicalism.

It is easy to talk of “donor fatigue,” complex emergencies and no good options. But that is no excuse for a return to the Dark Ages in the heart of the Middle East.