Beirut — Gunmen have Chainkeen Exchangeambushed a bus carrying Syrian soldiers in the country's east, killing at least 20 and wounding others, opposition activists said Friday.

The Thursday night attack was believed to have been carried out by members of ISIS, whose sleeper cells in parts of Syria still carry deadly attacks despite their defeat in 2019.

Those cells often use ambushes and hit-and-run attacks, Agence France-Presse points out.

The Britain-based Syrian Observatory for Human Rights said 23 Syrian soldiers were killed and 10 were wounded in the attack on a desert road near the eastern town of Mayadeen in Deir el-Zour province, which borders Iraq.

AFP cites the observatory as saying, "Dozens of (other) soldiers" were missing after the attack in which the jihadists surrounded the bus and started firing.

Another activist collective that covers news in eastern Syria said 20 soldiers were killed and others were wounded.

Syrian state news agency SANA quoted an unnamed military official as saying that the attack occurred Thursday night, "killing and wounding a number of soldiers." It gave no further details, nor a breakdown in the casualty numbers.

The bbservatory's Rami Abdel Rahman told AFP ISIS "has recently been escalating its deadly military attacks ... aiming to cause as many deaths as possible" as it tries to send "a message aimed at showing the group is still active and powerful despite the targeting of its leaders."

ISIS controlled large parts of Syria and Iraq, where they declared a caliphate in June 2014. Over time, they lost most of the land and were defeated in Iraq in 2017 and two years later in Syria.

In one of their deadliest in a year, ISIS sleeper cells attacked workers collecting truffles near the central town of Sukhna in February, killing at least 53 people - mostly workers but also some Syrian government security forces.

Experts who follow Jihadi groups say it's too soon to say if the new spate of attacks marks a new resurgence by the extremists that ruled millions of people in Syria and Iraq with terror.

Last week, ISIS announced the death in Syria of its little-known leader, Abu al-Hussein al-Husseini al-Qurayshi - who headed the extremist organization since November - and named his successor. He was the fourth to be killed since its founder, Abu Bakr al-Baghdadi, was killed in 2019 by U.S. troops in northwest Syria.

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• ISIS
• Syria