The strikes against the ISIL terrorists have been more intense than ever, said the Britain-based Syrian Observatory for Human Rights on Sunday.

"The Syrian air force has been pounding ISIL's bases, including those in the northern province of Raqqa and Hasakeh in the northeast," which borders Iraq, said the group, which is tied to anti-Damascus opposition groups outside the country.

In Raqqa, the air force bombed the area surrounding ISIL's main headquarters in Syria, as well as the group's so-called religious courts, said the Observatory, adding there were no reported casualties.

Photographs sent by an opposition group in Raqqa that could not be independently verified showed craters in the ground and rubble in front of the main gates of the headquarters, a former town hall.

This is while on Saturday, the Syrian army also bombarded ISIL's headquarters at Shaddadi in Hasakeh, home to a frontier crossing from Iraq that is under the terrorists’ control.

Observatory director Rami Abdel Rahman said the strikes were Syria's most "intense" against ISIL, and that they were being carried out "in coordination with the Iraqi authorities."

The government in Baghdad has been gearing up for a counter-offensive against ISIL in areas where it and other extremist militants have presence in northern Iraq.

ISIL espouses an extremist interpretation of Islam, and has in mind an ambitious plot to set up a state stretching across the Syria- Iraq border. It has been accused of committing widespread human rights abuses in Syria.

In 2013, it took part in operations against Syrian forces. But in recent months, it has exclusively fought against rival Syrian insurgents.

A war pitting Syrian militants against ISIL has killed more than 6,000 people, mostly insurgents, since it broke out in January.

NTJ/MB