Writing in Foreign Policy, Jimmy Carter and Mary Robinson argue that to help bring Israelis and Palestinians closer to peace, world leaders must recognise Hamas and pressure both sides to respect international law.

Israelis and Palestinians are still burying their loved ones as Gaza's third war in six years continues. Since 8 July, when this war began, more than 1,600 Palestinian and 65 Israeli lives have been sacrificed. Many in the world are heartbroken in the powerless certainty that more will die, that more are being killed every hour.

This tragedy results from the deliberate obstruction of a promising move toward peace in the region, when a reconciliation agreement among the Palestinian factions was announced in April. This was a major concession by Hamas, in opening Gaza to joint control under a technocratic government that did not include any Hamas members. The new government also pledged to adopt the three basic principles demanded by the Middle East Quartet comprised of the United Nations, the United States, the European Union, and Russia: nonviolence, recognition of Israel, and adherence to past agreements. Tragically, Israel rejected this opportunity for peace and has succeeded in preventing the new government's deployment in Gaza.

Two factors are necessary to make Palestinian unity possible. First, there must be at least a partial lifting of the 7-year-old sanctions and blockade that isolate the 1.8 million people in Gaza. There must also be an opportunity for the teachers, police, and welfare and health workers on the Hamas payroll to be paid. These necessary requirements for a human standard of living continue to be denied. Instead, Israel blocked Qatar's offer to provide funds to pay civil servants' salaries, and access to and from Gaza has been further tightened by Egypt and Israel.

There is no humane or legal justification for the way the Israeli Defense Forces are conducting this war. Israeli bombs, missiles, and artillery have pulverised large parts of Gaza, including thousands of homes, schools, and hospitals. More than 250,000 people have been displaced from their homes in Gaza. Hundreds of Palestinian noncombatants have been killed. Much of Gaza has lost access to water and electricity completely. This is a humanitarian catastrophe.

There is never an excuse for deliberate attacks on civilians in conflict. These are war crimes. This is true for both sides. Hamas's indiscriminate targeting of Israeli civilians is equally unacceptable. However, three Israeli civilians have been killed by Palestinian rockets, while an overwhelming majority of the 1,600 Palestinians killed have been civilians, including more than 330 children. The need for international judicial proceedings to investigate and end these violations of international law should be taken very seriously.

The UN Security Council should focus on what can be done to limit the potential use of force by both sides. It should vote for a resolution recognising the inhumane conditions in Gaza and mandate an end to the siege. That resolution could also acknowledge the need for international monitors who can report on movements into and out of Gaza as well as cease-fire violations. It should then enshrine strict measures to prevent the smuggling of weapons into Gaza. Early discussions have already taken place. The Elders, an international group of elder statesmen of which we are a part, hope these discussions will continue and reach fruition.

At the Palestinians' request, the Swiss government is considering convening an international conference of the signatory states of the Geneva Conventions, which enshrine the humanitarian laws of warfare. This could pressure Israel and Hamas into observing their duties under international law to protect civilian populations. We sincerely hope all states – especially those in the West, with the greatest power – attend and live up to their obligations to uphold the Fourth Geneva Convention, which governs the treatment of populations in occupied territory.

Unity between Fatah and Hamas is currently stronger than it has been for many years. As Elders, we believe this is one of the most encouraging developments in recent years and welcome it warmly. This presents an opportunity for the Palestinian Authority to reassume control over Gaza – an essential first step towards Israel and Egypt lifting the blockade.

The Palestinian Authority cannot manage the task of administering Gaza on its own. It will need the prompt return of the EU Border Assistance Mission, an international effort to help monitor border crossings that was launched in 2005 and suspended in 2007. EU High Representative Catherine Ashton has already offered to reinstate the program, covering not only Rafah but all of Gaza's crossings. Egypt and Israel would, in turn, cooperate with international monitors to be deployed in Gaza and along its borders, backed by a UN Security Council mandate to protect civilian populations. A valuable precedent for trust-building between Egypt and Israel is the international peacekeeping force operating in the Sinai, mandated by the peace treaty signed by the two countries in 1979.

The international community's initial goal should be the full restoration of the free movement of people and goods to and from Gaza through Israel, Egypt, and the sea. Concurrently, the United States and EU should recognise that Hamas is not just a military but also a political force. Hamas cannot be wished away, nor will it cooperate in its own demise. Only by recognising its legitimacy as a political actor – one that represents a substantial portion of the Palestinian people – can the West begin to provide the right incentives for Hamas to lay down its weapons. Ever since the internationally monitored 2006 elections that brought Hamas to power in Palestine, the West's approach has manifestly contributed to the opposite result.

Ultimately, however, lasting peace depends on the creation of a Palestinian state next to Israel.

Leaders in Israel, Palestine, and the world's major powers should believe that policy changes are within reach that would move Israelis and Palestinians closer to a day when the skies over the Holy Land can forever fall silent.

Versions of this article have been published in Foreign Policy, The Guardian and The Nation (Pakistan).