Fatalities reported after 'huge explosion' rocks Syrian capital

"The explosion took place near a security branch in the south of the city. There are some people killed and injured but we could not verify the toll immediately," the Britain-based Syrian Observatory for Human Rights told AFP.

It was unclear if the blast was caused by a bomb that was planted or a suicide attack, according to the monitor, which relies on a network of sources inside the country. However, shooting was reported following the explosion. 

Syrian state television earlier reported that a blast had been heard around the southern highway in Damascus. 

"First reports suggest a terrorist act," the broadcaster said, although it fell short of providing further information or details on the incident. 

Syria is locked in a civil war that has killed more than 360,000 people by official counts suspended in 2014, and much more by unofficial counts, and displaced millions since a brutal crackdown on anti-government protests in 2011 spiralled into full conflict. 

With key military backing from Russia, President Bashar al-Assad's forces have retaken large parts of Syria from rebels and jihadists, and now control almost two-thirds of the country.

The Syrian regime in May reclaimed a final scrap of territory held by the Islamic State group in southern Damascus, cementing total control over the capital for the first time in six years.

Observatory chief Rami Abdel Rahman said that Sunday's blast appeared to be the first attack in Damascus in over a year. 

Elsewhere in the country, nineteen people including four Americans were killed in a suicide bombing at a small restaurant in the flashpoint northern Syrian town of Manbij on Wednesday. It was the deadliest attack to hit US troops since they deployed to Syria in 2014 to assist local forces against IS. 

The attack prompted the US-led anti IS coalition to increase its airstrikes in the region, killing six civilians, four of which children, during an air raid on the Islamic State group's embattled enclave in eastern Syria on Friday.

Also on Friday, eleven people were killed after a bombing at an ammunition depot in the jihadist-held city of Idlib in northwestern Syria.

It targeted the arms store belonging to Hayat Tahrir al-Sham, an alliance led by Syria's former Al-Qaeda affiliate, the Syrian Observatory for Human Rights said.

The blast killed seven HTS fighters and four other people, the war monitor said.

Abdel Rahman said IS was likely responsible for the bombing, after HTS executed members of the extremist group the previous day.

The Manbij bombing rekindled controversy triggered by President Donald Trump last month with his surprise announcement of a full withdrawal from Syria.

The US president justified the order with the assertion that the jihadists had now been largely defeated" in Syria, a claim that the attack threw into renewed question.

Agencies contributed to this report.

Follow us on Twitter: @The_NewArab