The Daesh terrorist group claimed responsibility for killing 26 Syrian soldiers in the eastern Deir el-Zour province in an attack carried out on Thursday.

Despite losing its last piece of territory in Syria in 2019, Daesh has maintained hideouts in the vast Syrian desert from which it has carried out ambushes and hit-and-run attacks.

Daesh claimed the attack on Friday, saying it had carried out an ambush "on two military buses," targeting them "with heavy weapons and rocket-propelled grenades" and setting one on fire, according to a statement from the terrorists' Amaq news agency.

Daesh "members targeted a military bus" in Deir el-Zour province on Thursday, said the Syrian Observatory for Human Rights.

"The number of dead has risen to 26" soldiers, it said, calling it the extremists' deadliest attack on government forces this year.

The terrorists surrounded the bus in the desert near Mayadeen in Deir el-Zour province and opened fire, the observatory added.

Eleven other soldiers were wounded, with some in critical condition, said the Britain-based group, which relies on a network of sources inside Syria.

Syrian state news agency SANA said the "terrorist attack" had caused a number of military casualties, citing an unidentified army source.

Syrian regime forces and allied pro-Iranian armed militia deployed in the area were on high alert on Friday, the observatory reported.

The war monitor's Rami Abdel Rahman said Daesh "has recently been escalating its deadly military attacks... aiming to cause as many deaths as possible."

By doing so, the terrorists are trying to show that Daesh "is still active and powerful despite the targeting of its leaders," he told Agence France-Presse (AFP).

Last week, Daesh announced the death of its leader Abu al-Hussein al-Husseini al-Qurashi, who it said was killed in clashes in northwestern Syria.

A spokesperson for the group announced a new leader, known as Abu Hafs al-Hashimi al-Qurashi, in a recorded message on its channels on the Telegram messaging app.

In recent weeks, Daesh terrorists have increased their attacks in the north and northeast.

Thursday's attack was the third carried out by the terrorists this month alone.

Earlier this week, 10 Syrian soldiers and pro-government fighters were killed in a Daesh attack in the former terrorist stronghold of Raqqa province, the observatory said.

Last week, the terrorists attacked a convoy of oil tankers guarded by the regime forces in the Syrian desert, killing seven people including two civilians.

And last month, the terrorist group claimed responsibility for a rare bombing in Damascus that killed at least six people near the capital's Sayyida Zeinab mausoleum, Syria's most visited Shiite pilgrimage site.

The terrorist group's brutal rule was marked by beheadings and mass shootings.

Daesh has had five leaders since it lost the last remnant of large swathes of Syria and neighboring Iraq in 2014.

Four of them were killed, including the group's first leader, Abu Bakr al-Baghdadi, who died in a U.S. raid in October 2019.

Civil war first broke out in Syria after President Bashar Assad's regime crushed peaceful protests in 2011. It has since drawn in foreign powers and terrorists.

The conflict has killed more than half a million people and driven half of the country's prewar population from their homes, with many seeking refuge in neighboring countries.