The Islamic State group has executed at least 217 people, including civilians, in and around the ancient Syrian city of Palmyra in the last nine days, a monitor said Sunday.

The Syrian Observatory for Human Rights said it had documented the executions of 67 civilians, including children, and 150 members of regime forces by IS jihadists in different parts of Homs province since May 16.

Australia on Monday appointed a counter-terrorism chief to coordinate security agencies, while pointing to the United States and Britain to justify a proposal to strip citizenship from dual nationals linked to jihadists.

Like many countries, Australia is grappling with heightened threats from "home-grown" extremists with several alleged terror plots foiled this year inspired by the Islamic State group.

A Syrian brigadier-general was killed in a blast that targeted his car in downtown Damascus on Sunday, the Syrian Observatory for Human Rights monitor said.

The Britain-based group said "a brigadier general and approximately six people with him were killed in an explosion in the Adawi neighborhood in the center of the capital."

The Gulf Cooperation Council on Sunday rejected claims a U.S.-led coalition air campaign against the Islamic State group has failed following advances by jihadists in Syria and Iraq.

Speaking in Doha, after a meeting between foreign ministers of the GCC and European Union, Khalid al-Attiyah, Qatar's foreign minister, conceded that military action alone was not enough.

Weakened by years of war, Syria's government appears ready for the country's de facto partition, defending strategically important areas and leaving much of the country to rebels and jihadists, experts and diplomats say.

The strategy was in evidence last week with the army's retreat from the ancient central city of Palmyra after an advance by the Islamic State group.

Islamic State group supporters and a monitoring group said jihadists shot down a government helicopter in northern Syria early Sunday, but state media said the aircraft had suffered technical problems.

The Syrian Observatory for Human Rights said IS had brought down the helicopter after midnight near the Kweyris air base in the east of Aleppo province.

The Islamic State group took full control of a border crossing between Iraq and Syria Sunday, tightening its grip on the heart of its self-proclaimed caliphate.

The move gave IS control of the two main roads between Syria and Iraq's province of Anbar, as the jihadists pressed their most devastating offensive in months.

Interior Minister Nouhad al-Mashnouq criticized on Sunday the recent remarks of Hizbullah deputy Secretary General Sheikh Naim Qassem on “liberating” the northeastern border town of Arsal, saying that the army should be responsible for such a mission, reported the daily al-Mustaqbal.

He told the daily: “Qassem is calling for the destruction of Arsal, not its liberation.”

A number of Syrian opposition factions will gather in Cairo next month to form a new coalition as an alternative to an exiled West-backed alliance, officials said Saturday.

More than 200 figures from the armed and civilian opposition factions are to attend the June 8-9 gathering and discuss a roadmap aimed at ending the four-year war in Syria.

The head of the U.N. refugee agency appealed on Saturday to the international community to boost development aid countries hosting Syrian refugees such as Jordan and Lebanon.

"They are the first line of defense for global collective security and they are pillars, essential pillars, for regional security," Antonio Guterres told The Associated Press at a regional World Economic Forum conference held in Jordan.