Syrian President Bashar al Assad says his forces are "very close" to Islamic State's self-proclaimed capital, Raqqa - as the Syrian capital Damascus was hit by deadly twin bombings.

A US-backed militia alliance, the Syrian Democratic Forces (SDF), which includes Kurdish fighters, is also advancing towards the city, which IS has held since January 2014.

Syrian president Mr Assad, who is supported by Russian and Iranian forces, said another IS stronghold, the eastern city of Deir ez-Zor, could also be targeted at the same time as Raqqa.

Mr Assad told a Chinese TV station the war, which began as an uprising in 2011, would take "a few months" if "we don't have foreign intervention".

He said: "We always have hope that this year is going to be the last year. But at the end, this is war and you can't expect what is going to happen precisely."

His comments come as at least 40 people were killed and 120 others injured in twin bombings in Damascus' Old City.

The Iraqi foreign ministry said Shia pilgrims from Iraq, who were going to pray at a shrine, had been targeted.

A roadside bomb detonated as a bus passed and a suicide bomber blew himself up in what were rare attacks in the Syrian capital.

The Assad regime sees all armed opposition as terrorist groups and Mr Assad said all foreign troops on Syrian soil without invitation or consultation with the Syrian government are considered "invaders".

In Syria, Turkish forces have attacked Kurdish fighters, and hundreds of US troops are there to help the SDF prepare for the looming fight for Raqqa.

Mr Assad said Russia hopes it can bring the US and Turkey into co-operating with Moscow and Damascus in the fight against terrorism in Syria.

He said "in theory" he shared the same priority as US President Donald Trump of fighting terrorism, but they have had no formal contact yet.

There are also concerns over which fighters will retake Raqqa in the future.

US commanders are in favour of a mixed force of Syrian Arabs and the Kurdish YPG militia, while Turkey objects to arming the Kurds, who it claims are terrorists.