Syria’s Ministry of Health says at least nine killed and 20 others wounded after blast rips through busy cafe.

An explosion at a cafe in central Damascus has killed at least nine people and injured 20 others, according to Syria’s Ministry of Health.

The explosion was reported at around 3:24pm local time (12:24 GMT) on Thursday inside a cafe on al-Nasser Street in the al-Marjah district, close to the Palace of Justice, according to Syrian state media.

Syrian state television said the blast was caused by an explosive device.

Footage from the site showed severe damage to the cafe with blood smeared on the floor.

An investigation into the cause of the explosion has been launched with a number of government and private surveillance cameras in the area, said Milad Fadl, Al Jazeera’s Syria correspondent.

“Traces of blood are all over the ground; the Interior Ministry is trying to gather evidence to see who is responsible,” Fadl said.

“Residents in the area gave first aid to the injured until the ambulances arrived.”

Security forces initially cordoned off the area, fearing a secondary explosion.

They have not yet gathered enough evidence to identify a perpetrator, Fadl said, but security forces have been working to uncover sleeper cells operating in the country, seeking to destabilise the new government.

“They said there are parties who do not want stability in Syria and so will, from time to time, conduct operations like this,” said Fadl.

“Security forces have arrested other cells like this, like after [another explosion] and there have been several security operations that lead to arrests.”

The Palace of Justice, which lies about 40 metres (131 feet) away from the cafe, has held trials for high-profile members of the former al-Assad government.

This week, Syria’s former grand mufti, Ahmad Badr al-Aldin Hassoun, stood trial at the Palace of Justice.

Maher Marwan, the governor of Damascus, said that the security situation in the capital has improved in recent months, but it will take time for the Syrian state to guarantee complete stability.

“The more Syria attains stability, the more there are those who want to damage it,” Marwan told reporters near the site of the explosion.

“The coming hours will reveal everything and those who shed the blood of Syrians will pay, but Syria will be well as long as we are one hand and this will not shake the Syrian state,” he said.

The area was busy due to the trials and nearby marketplaces when the blast took place.

“When we arrived on the scene, a lot of people were gathered … Official government sources say the death toll could increase,” said Obaida Hitto, an Al Jazeera correspondent in Damascus.