The UN Security Council on Monday began fine tuning a draft resolution aimed at choking off the flow of foreign fighters and financial support to jihadists in Iraq and Syria.

Fighters from the extremist Islamic State(IS) have made dramatic gains in Iraq, prompting US President Barack Obama to order air strikes to halt their advance and air drops to help tens of thousands of fleeing civilians.

Experts from the 15-nation council met Monday to discuss the measure proposed by Britain with a view to adopting a strongly-worded text this week, sources said.

An early draft of the resolution seen by AFP threatens to draw up a sanctions black list of individuals, groups and entities who support the Islamic State in Iraq and the Levant (ISIL), which has since renamed itself simply Islamic State, and the Al-Nusrah Front in Syria.

The draft "calls on all member states to take national measures to suppress the flow of foreign terrorist fighters" to IS and Al-Nusrah and threatens to slap sanctions on those involved in recruitment.

It also warns governments that trade with the jihadists, who now control oilfields and other potentially cash-generating infrastructure, "could constitute financial support" that may lead to sanctions.

The council accuses the jihadists of carrying out atrocities, citing the targeting of civilians in Syria and mass executions, extrajudicial killings of Iraqi soldiers and targeted persecutions of religious minorities in Iraq.

It warned that such attacks may constitute a crime against humanity.

The draft resolution states that the Council is acting under chapter VII of the UN charter, which means the measures could be enforced by military force or economic sanctions.

Negotiations on the resolution forged ahead as Iraqi President Fuad Masum tasked Haidar al-Abadi to form a new government able to lead the fight against the jihadists, sidelining Nuri al-Maliki who had been prime minister since 2006.

The council on Thursday adopted a unanimous statement calling on governments to help Iraq cope with a humanitarian crisis sparked by a jihadist offensive.

That statement from the council was the third strong condemnation in recent weeks of the IS offensive that saw jihadists seize control of the main northern city of Mosul on June 10.