The United Nations security council agreed on Wednesday to launch a concerted effort to staunch the flow of radicalised jihadists from around the world to the cause of Islamic State and other terrorist groups.

In a rare session of the security council attended by heads of state – only the sixth of its kind in the organ’s 68-year history – all 15 member states voted for a US-backed resolution that seeks to step up the battle against “foreign terrorist fighters”, as US president Barack Obama described them.

The agreement from the world body’s highest panel was designed to tackle, Obama said, the new threat of the “unprecedented flow of fighters in recent years to conflict zones, most recently Syria and Iraq”.

He added: “These terrorists exacerbate conflicts; they pose an immediate threat to people in these regions; and as we’ve already seen in several cases, they may try to return to their home countries to carry out deadly attacks.”

Western governments, as well as Arab states neighbouring Syria and Iraq that have provided the majority of foreign fighters, have grown increasingly alarmed in recent months about the steady flow of their citizens to the Isis cause. Precise figures are not known, but Obama put the figure higher than previously stated at more than 15,000 fighters from at least 80 countries.

Of those, the New York-based intelligence analysts the Soufan group has estimated that the lion’s share of fighters have come from Jordan, Saudi Arabia and Tunisia, each of which have been the source of more than 2,000 jihadists.

Europe is also thought to have provided about 1,000 fighters, with the UK source of 500 and Belgium at least 250. The US has put the figure of its foreign fighters at about 100.

The British prime minister David Cameron said that the threat of foreign fighters was “far greater today than it has ever been in previous conflicts”. He said British people were “sickened” by the recent beheadings of a British aid worker David Haines and American journalists James Foley and Stephen Sotloff by an Isis extremist with an apparent British accent, actions that were “the very opposite of what our peaceful, tolerant country stands for”.

In particularly strong language, Cameron said that the “cruelty being meted out – beheadings, eyes being gouged out, rape – is horrific. It is literally mediaeval in character. But one of the most disturbing aspects is how this conflict is sucking in our own young people, from modern, prosperous societies.”

Facebook Twitter Pinterest British PM David Cameron. ‘The cruelty being meted out is horrific.’ Photograph: Spencer Platt/Getty Images

He listed some of the tough measures that the UK government was taking to target potential jihadists travelling from Britain to join Isis and the al-Nusra Front. They included a move to make it easier for the state to seize the passports of suspects or prevent them temporarily from re-entering the country; pressure on airlines to comply with no-fly lists and security screening; and new powers for the police to impose “stronger locational constraints on those in the UK who pose a risk”.

Cameron also called on governments to ban those he called “preachers of hate” from entering their countries and spreading the “poisonous ideology of extremism”.

The French president, François Hollande, put the estimate for the number of fighters that have come from his country at 1,000, saying their ranks had mushroomed by 50% since the beginning of the year.

“So our response must be rapid and lasting,” Hollande said. He added that his government would make additional moves to prevent radicalised people leaving France in the first place, and to close down jihadist websites.

Hollande referred to the beheading this week of Hervé Gourdel, a French tourist, by Algerian extremists connected to Isis. He said that “no country is safe from this threat,” adding that in some cases whole families had left their homes to travel to join the jihadist cause.

Under the terms of the resolution, all the UN’s member states must “prevent and suppress the recruiting, organizing, transporting or equipping of individuals” who travel to another country to take part in terrorist acts or training. States must also “prevent the movement of terrorists or terrorist groups” through their territory “by effective border controls and controls on issuance of identity papers and travel documents”.

The move against foreign fighters was bolstered by the decision taken earlier this week to focus on a small number of prominent foreign fighters and funders of jihadist causes in Iraq, Syria and other hotspots. A committee of the security council that deals with al-Qaida related sanctions imposed tough penalties on 11 individuals from France, Norway, Saudi Arabia, Kuwait and Senegal.

Like much of the work of the UN, the impact of the new resolution championed by Obama will depend for its impact upon the political will of each individual member state. The US president stressed that 104 countries around the world had sponsored the resolution.

Several heads of state at the security council meeting expressed their resolve to step up measures against potential jihadists from their countries. King Abdullah II of Jordan, which took part in the recent US airstrikes on Isis positions in Syria, said his country could be counted on “to play our part”. He said the scourge of extremists recruiting around the world through the use of social media was a threat that would effect “every delegate here and beyond. It is the fight of our times”.

It was a sign of the united will of the international community that even the US and Russia, who have been sliding into an increasingly belligerent relationship in recent months, for once found themselves on the same side of the argument. Sergey Lavrov, the Russian foreign minister, said that his country backed the mission to “choke off any actions of foreign terrorist fighters”.

The unanimous tone of the security council debate was countered outside the UN building by human rights groups who warned that a ramping up of state intervention against potential jihadists could have implications. Human Rights Watch said the push risked repeating the mistakes of the post-9/11 era.

“The resolution says nothing about due process protections, yet calls on states to apprehend people at borders. It does nothing to prevent governments from carrying out abusive counterterrorism policies and practices,” said the group’s Andrea Prasow.