The horrific war in Syria continues to worsen and bleed beyond its borders. A cold calculation seems to be taking hold: that little can be done except to arm the parties and watch the conflict rage.

The death toll may now be well over 150,000. Prisons and makeshift detention facilities are swelling with men, women and even children. Deaths by summary execution and unspeakable torture are widespread. People are also dying from hunger and once rare infectious diseases. Whole urban centres and some of humankind's great architectural and cultural heritage lie in ruins. Syria today is increasingly a failed state.

The United Nations has tried hard to address the conflict's deep roots and devastating impact. Our humanitarian and other efforts are saving lives and reducing suffering. But our fundamental objective – an end to the conflict – remains unmet. The bleak prospects for peace have darkened further with the flare-up of violence and sectarian tensions in Iraq. The cohesion and integrity of two major countries, not just one, are in question.

But the international community must not abandon the people of Syria and the region to never-ending waves of cruelty and crisis. The following six points can chart a principled and integrated way forward.

1. Ending the violence

Residents wait for UN food aid at al-Yarmouk camp south of Damascus. Photograph: Handout/Reuters

It is irresponsible for foreign powers to give continued military support to parties in Syria that are committing atrocities and flagrantly violating fundamental principles of human rights and international law. I have urged the United Nations security council to impose an arms embargo. The sides will have to sit across from each other again at the negotiating table. How many more people must die before they get there?

2. Protecting people

The UN manages a huge humanitarian relief effort. But the Syrian government continues to impose unconscionable access restrictions; it has removed medical supplies from aid convoys and deliberately starved and collectively punished communities it regards as sympathetic to the opposition. Some rebel groups have acted similarly. Moreover, the international community has provided barely a third of the funding needed for the relief effort. I continue to appeal for an end to the sieges and for unfettered humanitarian access across internal frontlines and international borders.

3. Starting a serious political process

The warring parties systematically blocked the relentless initiatives of two of the world's leading diplomats, Kofi Annan and Lakhdar Brahimi. The presidential election earlier this month was a further blow, and failed to meet even minimal standards for credible voting. I will soon name a new special envoy to pursue a political solution and a transition to a new Syria. Regional countries have a special responsibility to help end this war. I welcome recent contacts between Iran and Saudi Arabia, and hope that they will build confidence and reverse a destructive competition in Syria, Iraq, Lebanon and elsewhere. Syrian civil society groups are making courageous efforts to maintain the fabric of society and keep open channels of solidarity and communication.

4. Ensuring accountability for serious crimes

Refugees cross from Syria to Turkey via the Orontes river in December 2012. Photograph: Manu Brabo/AP

Last month, a resolution that aimed to refer the conflict to the international criminal court failed to pass the security council. I ask those member states that say no to the ICC, but say they support accountability in Syria, to come forward with credible alternatives. The Syrian people have a right to justice and action against impunity.

5. Finishing the destruction of chemical weapons in Syria

The UN and the Organisation for the Prohibition of Chemical Weapons have worked together to destroy or remove from the country all of the declared materials in a once large arsenal. Many member states have provided critical resources and support for this challenging task, which was undertaken in an active war zone and which will now be completed at various destruction facilities outside Syria. While almost all of the killing in Syria is being done with conventional weapons, it has been essential to reinforce the global norm banishing the production and use of chemical weapons.

6. Addressing the regional dimensions of the conflict, including the extremist threat

Foreign fighters are in action on both sides, increasing the level of violence and exacerbating sectarian hatreds. While we should not blindly accept the Syrian government's demonisation of all the opposition as terrorists, neither should we be blinded to the real threat of terrorists in Syria. The world must come together to eliminate funding and other support for Jabhat al-Nusra and the Islamic State of Iraq and al-Sham. The latter is also a threat to all communities in Iraq. It is crucial for the region's leaders, political and religious, to call for restraint and to avoid a spiral of attack and reprisal.

Syrian refugees at a protest against Bashar Al-Assad at a refugee camp in Antakya, Turkey, in March 2012. Photograph: Aykut Unlupinar/Anadolou/EPA

For the moment, the greatest obstacle to ending the Syrian war is the notion that it can be won militarily. I reject the current narrative that the government of Syria is "winning". Conquering territory through aerial bombardments in densely populated civilian neighbourhoods is not a victory. Starving besieged communities into surrender is not a victory. Even if one side were to prevail in the short term, the devastating toll will have sown the seeds of future conflict.

Dangerous sectarian tensions, massive movements of refugees, daily atrocities and spreading instability make the civil war in Syria a global threat. All the values for which we stand, and all the reasons for which the UN exists, are at stake across the devastated landscape that is Syria today. The time is long past for the international community, in particular the security council, to uphold its responsibilities.