BEIRUT — Militants in Syria have threatened to execute Lebanese servicemen they hold captive unless Lebanon releases the ex-wife of the Islamic State group's leader and another militant-linked woman, a negotiator said Tuesday. Salafist Sheikh Wissam Al-Masri is mediating the release of 25 police and soldiers held by IS and the Syrian branch of Al-Qaeda, the Al-Nusra Front. Masri told reporters IS wrote a letter to him demanding the release of Saja Al-Dulaimi, the former wife of IS leader Abu Bakr Al-Baghdadi, as well as Ola Sharkas, the wife of Al-Nusra commander Anas Sharkas. The militants also called for “the liberation of all female Muslims detained in Lebanon in connection to the war in Syria,” Masri said. Lebanese authorities announced earlier this month the arrests of Dulaimi and Sharkas's wife. Dulaimi had tried to enter Lebanon from Syria with two sons and a daughter, the interior minister said. The soldiers and police were captured when Syria-based militants briefly overran the Lebanese border town of Arsal in August. The fighters withdrew after a truce negotiated by clerics, but took 30 hostages. Four have since been executed, while a fifth died from his injuries in captivity. Meanwhile, a powerful blast from explosives planted in a tunnel under the Old City of Aleppo, in northern Syria, killed seven government troops Tuesday, a monitor said in a new toll. Jabha Shamiyeh, a new rebel coalition in Aleppo, was behind the blast, said the Syrian Observatory for Human Rights. Observatory chief Rami Abdel Rahman said at least seven government troops and allied fighters were killed. An earlier statement from his group had put the toll at 20 dead or wounded. — Agencies