World leaders are set to reject a concrete target for the number of refugees that should be resettled within developed countries, dashing hopes of a solution to the world’s unprecedented displacement crisis.

Before a landmark conference in September, negotiators from every UN member country have failed to agree on a promise to share responsibility for 10% of the world’s refugee population, and postponed the completion of a new global refugee deal for another two years.

With the number of refugees and displaced people around the world at an all-time high, campaigners had hoped that an international conference on refugees and migrants in New York would enable world leaders to agree a new mechanism for sharing refugees.

Currently, 86% of refugees live in the developing world. This has led to calls for richer nations to shoulder a greater responsibility for the displacement crisis. A failure to provide refugees with legal routes to the developed world also contributed to the decision by over a million asylum seekers to travel to Europe by irregular means in 2015.

But in a collective pre-summit statement completed this week, negotiators removed an earlier promise to move one in 10 refugees to the developed world, leaving only vague language that praised the principle of shared responsibility.

“We intend to expand the number and range of legal pathways available for refugees to be admitted to, or resettled in, third countries,” the statement said – stopping short of any concrete numbers.

Lebanon was among the countries to criticise the vague language, a source present at the negotiations said. Lebanon currently shoulders a refugee community vastly at odds with its tiny indigenous population, sheltering around 1.2 million refugees within a population of 4.5 million. In 2015, a fractionally smaller number of asylum seekers reached the European Union, which has a population of more than 500 million.

The UN refugee agency nevertheless hailed the negotiations, taking strength from the fact that diplomats had at least reaffirmed the principle of resettlement, despite a toxic global discourse on migration.

Volker Türk, UNHCR’s assistant high commissioner for protection, told the Guardian: “You can look at this from a glass-half-full or glass-half-empty perspective – and for us it’s a glass-half-full.”

Türk added: “In a situation where you have elections that are now won by demonising migrants and in a climate where major host countries such as Lebanon, Pakistan, Kenya and others are feeling that they don’t get the support that they need, in an environment where we have such polarised discussion at a domestic and also a regional and global level – I think it’s a minor miracle what we have seen come out as a draft for adoption.

“It reaffirms the 1951 refugee convention, it reaffirms the institution of asylum, it reaffirms the principle of non-refoulement, of non-return [of refugees to dangerous environments] – and these are important legal principles that a number of politicians have in the past questioned.”

But rights groups have criticised the agreement, arguing that world leaders have missed a historic chance to deal with one of the world’s most pressing crises.

Audrey Gaughran, director of global issues and research for Amnesty International, said: “It’s extremely disappointing – there’s almost no responsibility shared. They have lost a huge opportunity.”

Charlotte Phillips, an adviser on refugee policy at Amnesty, added: “For us this was the opportunity for leaders to show strength and courage to tackle the crisis head on – but instead what we have is a document with very little concrete in it. Given the [scale of the] global refugee crisis as it stands, that is pretty pathetic.”

Other parties saw small victories in the pre-summit negotiations. The International Organisation for Migration (IOM), the world’s top migrant-focused aid group, is pleased that the summit will see it become formally affiliated with the UN. IOM sees this as belated but essential recognition that migration is an important enough global phenomenon to warrant its own UN agency.

Leonard Doyle, IOM’s chief spokesman, said: “One could quite easily dismiss the summit, but it is, at the end of the day, very significant that the UN is finally looking at the issue of migration in some complexity. It’s high time that an organisation specialising in migration – an advocate for migration and migrants – is at the table, sharing its expertise, and given a voice.”

But others still see September’s UN summit as a missed opportunity, with a decision on changes to the global refugee regime postponed to 2018. Attention now turns to another refugee-themed summit in New York scheduled for the same week in September, when leaders invited by Barack Obama will be invited to make individual resettlement pledges – as opposed to making collective ones.

“Refugees can’t wait till 2018 for states to do anything remotely useful – so we’re going to push for individual states to do more, and to open up new resettlement programmes,” said Amnesty’s Gaughran, who has released a five-point resettlement plan for world leaders to consider.