The Islamic State of Iraq and the Levant (ISIL) has continued to gain ground in northern Iraq despite weeks of US-led air strikes, and is now moving closer to the Iraq-Kurdish city of Erbil.

ISIL fighters are battling Kurdish volunteer troops in the town of al-Kuwayr, about 60km southwest of Erbil.

However, national security expert Douglas Ollivant, of the New America Foundation, told Al Jazeera on Tuesday that for now there was no immediate threat of ISIL closing in on Erbil.

Ollivant said that it is likely that the armed group will concentrate on al-Kuwayr, as they face a stronger resistance from Kurdish fighters and US-led air power should they make their way further into Kurdish areas.

"There are significant defences between these towns and Erbil," he said. "Erbil and Baghdad are still safe at this point."

In the neighbouring province of Nineveh, Provincial Governor Atheel al-Nujaifi told Al Jazeera that he is coordinating with the Iraqi defence ministry to set up a force to liberate Mosul from ISIL.

"It is the time to start work on the exact plan to liberate Mosul," Nujaifi said, as he appealed for more weapons and resources to fight the armed group.

"It's a miserable situation now in Mosul," he said. "There's no electricity, no water and no healthcare."

'Systematic executions'

Just south of Mosul in Anbar Province, ISIL continued on Tuesday to lay siege to more than 500 families belonging to the Albu Nimr tribe in the town of Heet.

It has been reported that in recent days, over 200 tribe members have been executed, over old grudges since the tribe had been suspected of siding with US and Iraqi forces in the past.

Government officials told Al Jazeera that a "systematic executions" of the members of the tribe is still under way.

The officials said that they have found a mass grave in an isolated desert area north of Ramadi.

Between 2006 and 2007, the tribe members formed armed groups, called "Awakening councils" to fight al-Qaeda in Heet with the support and backing of the US.

Day of mourning

In the southern province of Karbala, huge crowds of Shia Muslims gathered to mark Ashoura, under tight security and in defiance of threats of more attacks from ISIL.

The commemoration passed without any major attacks across the country, but local media reported at least two explosions south of Baghdad.

Al Jazeera, however, cannot independently verify the number of people killed or wounded.

Sunni ISIL fighters long consider the Shia as heretics and have targeted them in deadly attacks, killing more than 40 people in Baghdad in the 48 hours preceding Ashoura.

The commemoration marks the killing of Imam Hussein, the grandson of the Prophet Muhammad, by the army of Caliph Yazid in 680 AD, which helped solidify the divide between what would become the Sunni and Shia branches of Islam.

Source: Al Jazeera and agencies