The conflict in Syria has left more than 220,000 dead since it began four years ago with an uprising against President Bashar Assad, a key monitoring group said Thursday.

"We have counted 222,271 deaths since the start of the revolt in March 2011," the head of the Syrian Observatory for Human Rights, Rami Abdel Rahman, told Agence France Presse.

General Security chief Maj. Gen. Abbas Ibrahim told Palestinian factions and officials form the Palestinian joint security force that it was important to preserve the security of the southern camp of Ain el-Hilweh, sources said.

“The security of the camp is part of the security of Lebanon and Arabs,” Ibrahim said during a meeting he held with the two sides on Wednesday, according to the Palestinian sources.

Prominent leaders affiliated to the Islamic State of Iraq and the Levant (ISIL) reportedly retreated from the northeastern border town of Arsal to Syria's Riqqa.

According to the pan-Arab daily Asharq al-Awsat published on Thursday, ISIL's command decided to limit its presence in Arsal and its outskirts to 200 fighters and a single leader, spiritual judge Abou Balqis.

Two Canadian students appeared in a Montreal court Wednesday over fears they were plotting to commit crimes related to "terrorism," CBC's Radio-Canada said.

El Mahdi Jamali and Sabrine Djaermane, both 18, were ordered to remain in custody.

A U.N. envoy will travel to Iraq and Syria this week to address the disturbing use of rape, sex slavery and other sexual violence by extremists like the Islamic State.

Zainab Hawa Bangura, the special envoy on sexual violence in conflict, will also travel to Jordan, Turkey and Lebanon in her first Middle East tour.

Police in Bosnia on Wednesday arrested a man on terrorism charges for allegedly meeting with Islamic State jihadists in Syria.

The suspect, named as Kenan Krso, was suspected of "several activities linked with terrorism," a spokesman for the public prosecutor's office told reporters.

Rebels fighting in southern Syria will not cooperate militarily with al-Qaida's Syrian affiliate, al-Nusra Front, a spokesman said Wednesday.

Essam al-Rayes' comments come after tensions between local rebel groups and al-Nusra over the capture of a border crossing between Syria and Jordan.

Baghdad has announced its next battle against the Islamic State group is retaking Anbar province, but analysts say entrenched jihadists and limited Iraqi forces put a full reconquest out of reach for now.

Anbar is by far Iraq's largest province, shares a border with jihadist-held territory in Syria and has historically been a difficult area to control.

At least 24 people have been killed in a series of Syrian government air strikes around the city of Idlib, which rebels seized earlier this month, a monitoring group said Wednesday.

Two children were among 12 people killed when a barrel bomb hit a shelter in the rebel-held town of Saraqeb, southeast of Idlib, on Tuesday, the Syrian Observatory for Human Rights said.

British police have arrested six people on suspicion of terrorism after Turkish authorities stopped a group crossing the Syrian border, police said.

Four people aged between 22 and 47 were arrested at Manchester airport in north west England early Wednesday, following on from the arrest on Tuesday of a 21-year-old man at Birmingham airport in central England and a 31-year-old man in Rochdale, near Manchester.