At least 23 Syrian soldiers have been killed in an attack blamed on Islamic State (IS) militants in eastern Syria, reports say.

The jihadists surrounded a military bus in eastern Deir al-Zour province before opening fire, the UK-based Syrian Observatory for Human Rights said.

More than 10 other soldiers were injured and dozens are said to be missing.

The attack has been described as the deadliest this year by IS militants.

Despite losing the last of its territory in 2019, IS still maintains hideouts in the vast Syrian desert, from which it carries out ambushes and hit-and-run attacks.

Sana news agency quoted a military source saying a “terrorist” group had attacked a military bus on Thursday in the steppe desert on the road from the T2 pumping station – which lies close to the Iraqi border south of the city of Deir al-Zour – leaving a number of army personnel dead and injured.

The T2 pumping station was an IS stronghold until its capture by the Syrian army in 2017.

The Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group that relies on a wide network of sources on the ground in Syria, said the death toll was likely to rise.

Earlier this week, 10 Syrian soldiers and pro-government fighters were killed in an IS attack in the former jihadist stronghold of Raqa province, the SOHR said.

IS members have increased their attacks in Syria’s north and north-east in recent weeks.

The former suspected leader of the IS group in Syria, Abu Hussein al-Qurayshi, was killed by Turkish forces in April, the country’s president said.

IS once held 88,000 sq km (34,000 sq miles) of territory, stretching from north-eastern Syria across northern Iraq, and imposed its brutal rule on almost eight million people.

The group was driven from its last piece of territory in 2019, but the UN has warned that it remains a persistent threat.