Canada conducted airstrikes on Islamic State positions in Iraq for the first time on Sunday, while reports emerged that the jihadist group had executed more than 200 tribespeople in recent days.
"Today's strike demonstrates our government's firm resolve to tackle the threat of terrorism and to stand with our allies against ISIS' atrocities against innocent women, children and men," Canadian defense minister Rob Nicholson said in a statement.
Canada joined the anti-IS coalition on Thursday and conducted two days of reconnaissance before sending two CF-18s to attack jihadist positions around the city of Fallujah.
The attacks followed reports that IS had slaughtered scores of people from the Albu Nimr tribe, which had taken up arms against the insurgents.
Women and children were said to be among those executed over the past 10 days in western Iraq's Anbar province which has been largely over-run by IS.
Iraq is bracing for yet more violence in the coming days as hundreds of thousands of Shiites prepare to travel to shrines in Karbala for a major annual pilgrimage.
IS, a Sunni extremist group that has seized large parts of Iraq and Syria, is expected to target Ashura pilgrims, and 19 people died in attacks on Shiites on Sunday.
String of setbacks
Accounts varied as to the number and timings of the executions in Anbar, but all sources spoke of more than 200 people murdered in recent days.
Police Colonel Shaaban al-Obaidi told AFP that more than 200 people were killed, while Faleh al-Essawi, deputy head of Anbar provincial council, put the toll at 258.
The killings are probably aimed at discouraging resistance from powerful local tribes in Anbar.
IS also detained dozens of members of the Jubur tribe in Salaheddin province, north of Baghdad, officials and a tribal leader said.
Jubur tribesmen and security forces have been holding out for months against IS in the provincial town of Dhuluiyah.
Pro-government forces have suffered a string of setbacks in Anbar in recent weeks, prompting warnings that the province, which stretches from the borders with Jordan and Saudi Arabia to the western approach to Baghdad, could fall entirely.
Security forces who wilted before a lightning IS offensive in June are fighting to retake territory seized by the jihadists in Iraq's Sunni Arab heartland.
IS has declared an Islamic "caliphate" in territory it controls, imposing its harsh interpretation of sharia law and committing widespread atrocities.
Like other Sunni extremist groups, IS considers Shiites to be heretics and frequently attacks them, posing a major threat to the Ashura religious commemorations which peak on Tuesday and will be a major test for the new government headed by Prime Minister Haidar al-Abadi.
Two car bombs targeting Shiites in Baghdad ahead of Ashura killed at least 19 people on Sunday, officials said, while a city centre car bombing near a police checkpoint killed at least five.
On the Syria-Turkey border, meanwhile, some 150 Iraqi peshmerga fighters were preparing to bolster fellow Kurds in battling IS for the town of Kobane, after crossing the frontier late on Friday.
Syrian Kurdish militia have held off an IS offensive there for more than six weeks, and Kobane has become a crucial symbol in the anti-jihadist struggle.
Coalition air strikes
The Syrian Observatory for Human Rights, a Britain-based monitor, reported fierce clashes in the town's centre, north, south and Kurdish fighters shelling IS positions to its east.
Prior to Canada's airstrikes, the US-led coalition carried out at least three air raids near Kobane early on Sunday, according to the Observatory which relies on a wide network of sources inside the country.
At least 11 jihadists were killed in those strikes and fighting on Saturday, it said.
The Pentagon said five air strikes near Kobane on Saturday and Sunday hit five small IS units and destroyed three vehicles.
Canada declined to detail damage caused to the targets during its approximately four-hour mission. Details are expected at a news conference on Tuesday.
Canada's airstrikes come after a gunman whose name was on a terror watch list killed a soldier and attempted to storm Canada's parliament last month. The attack was one of two targeting Canadian soldiers just days apart.
Elsewhere in Syria, the Observatory said al Qaeda affiliate Al-Nusra Front seized a town and several villages in Idlib province late Saturday, in another blow to Western-backed rebels in the northwest.
It said Al-Nusra captured Khan al-Subul after the withdrawal of the Hazm movement, a moderate opposition group.
Al-Nusra also seized another five villages in Idlib held by Islamist and moderate rebel groups.
The advance comes a day after Al-Nusra seized the Idlib bastion of the Syria Revolutionaries Front, another Western-backed opposition group.
The advance of the al Qaeda affiliate is seen as a setback to US efforts to create and train a moderate rebel force as a counterweight to jihadists and the forces of Syrian President Bashar al-Assad.