Damascus, Aug 27 : Eleven Syrian military personnel were killed, and 20 others were injured in a rebel attack in the country's northwestern province of Idlib, a war monitor reported. The attackers carried out an assault and detonated explosive devices concealed in tunnels beneath Syrian Army positions in the southern countryside of Idlib, said the Syrian Observatory for Human Rights on Saturday. The observatory added that the attackers are from factions, including the Ansar al-Tawhid group and the Turkestan Islamic Movement, both affiliates of the Hayat Tahrir al-Sham (HTS) rebel group, Xinhua news agency reported. Tension has been brewing between the HTS and the Syrian Army, with both sides exchanging fire in northern Syria. On Friday, seven HTS members were killed by the army forces in the western countryside of Aleppo in northern Syria, according to the observatory. On Monday, Syrian forces intercepted and shot down three weaponised drones dispatched by the HTS in the northwestern provinces of Idlib and Hama, according to the state news agency SANA. On the same day, Russian airstrikes conducted in the Idlib region killed eight HTS militants, according to the observatory. HTS, previously known as the al-Qaida-linked Nusra Front, has established control over a large swathe of Idlib. /IANS