At least 11 Syrian soldiers were killed on Saturday and 20 others were wounded during a major attack launched by two jihadist groups in northwestern Syria, a non-governmental organization said.

The attack, which was not reported in official Syrian media, comes in response to Russian airstrikes on Thursday in the Jesr al-Sugur region near Idlib, where many Turkestan Islamic Party (TIP) fighters are active, according to with the Syrian Observatory for Human Rights.

“Eleven Syrian soldiers were killed and 20 others were wounded when Ansar al-Tawhid and TIP fighters blew up tunnels dug under army positions and carried out a simultaneous attack from other tunnels on the southern side of Idlib,” said the director of the Syrian Rami Abdel Rahman Observatory.

“Two jihadists took their own lives during the dual operation, while violent clashes continue, which is expected to raise the death toll,” said the NGO, which is based in Britain and has a very large network of sources in the war-torn country.

TIP members, who are mostly from China’s Uyghur Muslim minority, traveled to Syria after 2011 to help jihadist groups, notably Hayat Tahrir al-Sham (HTS) dominated by its former offshoot Al Qaeda in Syria.

– Two children dead –

Late on Saturday afternoon, two children — a girl and her brother — were killed and five other civilians were wounded by shelling by the Russian air force and Syrian government forces in Kanshafra, Jabal al-Zawiya district, south of Idlib, according to the White Helmets, the rescue teams that operate in rebel areas.

The bodies of the two children were later buried by their family, according to an AFP photographer at the scene.

The Syrian army is supported by the Russian air force which is shelling the Jabal al-Zawiya region, the Observatory said.

Backed by Moscow and Tehran, Syrian government forces have regained most of the territory they lost at the start of the war.

The last enclave of the armed opposition includes a large part of Idlib province and territories bordering Aleppo, Hama and Lattakia provinces.

In recent weeks, the region has seen an escalation of bombardment, mainly by the Russian air force, in response to HTS attacks, sometimes with drones, against areas under the control of the Syrian army in northwestern Syria, according to the Observatory.

The war in Syria already has half a million dead and millions displaced.