US officials have asked the Syrian opposition to call on the international community to hit positions belonging to the Islamic State group and help rebels eliminate the self-declared jihadists, Al Jazeera has learned from sources inside the opposition.

The Syrian National Coalition, the main political opposition bloc, and the leadership of the Free Syrian Army, a loose conglomeration of armed rebel, are expected to make the appeal from Turkey on Saturday, the sources said.

The news come as the US is carrying out air strikes on Islamic State targets in Iraq and a day after the UN Security Council unanimously adopted a resolution that aims to weaken the Islamic State and al-Nusra Front, al-Qaeda's Syria branch.

Commenting on the resolution, the Syrian Coalition's Special Representative to the UN, Najib Ghadbian, said: "The Syrian Coalition calls for targeted air strikes in Syria. Strikes should be backed up by intensive train and equip programmes for the moderate Syrian opposition forces that have been effectively fighting ISIS [Islamic State] for over a year."

Another member of the coalition told Al Jazeera that the group was "getting different promises" from the US.

The Islamic State, an al-Qaeda splinter group, has in the recent months seized swaths of territory in Iraq and Syria and declared a caliphate.

In Syria, the group enforced its rule in the province of Raqqa and other eastern parts of the country through conducting public executions and imposing strict social codes that have many residents living in fear while others have been forced to flee their homes.

Activists who stood up against the rule of the Islamic State have been met by a brutal crackdown. Many of those activists had already been campaigning for the fall of President Bashar al-Assad's rule since 2011.

Opposition politicians in exile have expressed dismay as to why three years of bloodshed has not led to the same rapid response by the international community as the escalating crisis in Iraq.

The Islamic State's swift push to the borders of Iraq's autonomous ethnic Kurdish region and towards Baghdad prompted President Barack Obama to authorise airstrikes on the group's strongholds earlier this month. Since then, US military aircraft have carried out several bombings and air-dropped food and water to help tens of thousands of civilians fleeing the fighters' advance.

On Saturday morning, the US launched more air strikes on positions belonging to the Islamic State in northern Iraq, according to the Kurdish news agency Roodaw.

Sanctions against 'emirs'

Friday's resolution named six people who will be subject to an international travel ban, asset freeze and arms embargo, including Islamic State spokesman Abu Muhammad al-Adnani, an Iraqi described by UN experts as one of the group's "most influential emirs" and close to its leader Abu Bakr al-Baghdadi.

The Security Council resolution "deplores and condemns in the strongest terms the terrorist acts of ISIL [Islamic State] and its violent extremist ideology, and its continued gross, systematic and widespread abuses of human rights and violations of international humanitarian law".

The resolution, drafted by Britain, condemned the recruitment of foreign fighters and expressed readiness to blacklist people financing or facilitating travel of foreign fighters.

The resolution is under Chapter 7 of the UN Charter, which makes it legally binding for UN member states and gives the council authority to enforce decisions with economic sanctions or force. However, it does not mandate military force to tackle the fighters.