In a speech to party faithful, Harper unequivocally branded the al-Qaida splinter group known as the Islamic State of Iraq and the Levant, or ISIL, as "evil" and "vile," saying it must be opposed.
Harper also reaffirmed the Conservative government's unwavering support of Israel "through fire and water" as he linked the fight against ISIL's extremism to Canada's support for the Jewish state.
Harper also blasted Russian President Vladimir Putin for his continued aggression in Ukraine, and pledged that Canada would loudly brandish its pro-Ukrainian solidarity later this week when President Petro Poroshenko visits Parliament Hill.
Harper's tough foreign policy rhetoric punctuated his speech to Conservative supporters to mark the return of the House of Commons from a summer recess. It also serves as a harbinger of what's to come when he speaks to the United Nations General Assembly next week in New York City.
But Harper's earnest denunciation of ISIL puts some distance between himself and Foreign Affairs Minister John Baird, who recently travelled to Iraq to bolster a new central government struggling to contain the Islamist insurgency.
"Canadians are rightly sickened by ISIL's savage slaughter of anyone who doesn't share their twisted view of the world. We know their ideology is not the result of 'social exclusion' or other so-called 'root causes,'" Harper said to a ripple of laughter.
"It is evil, vile, and must be unambiguously opposed."
The remark appeared to be aimed at Liberal Leader Justin Trudeau, who spoke about terrorism's "root causes" in the wake of last year's Boston Marathon bombing. Without naming him at the time, Harper lashed out at that view, saying when it comes to terrorist attacks people should not "sit around trying to rationalize it" or "figure out its root causes."
For his part, Trudeau brushed aside the issue, saying he supports Canada's multilayered support of the Iraqi people, including military and humanitarian assistance.
Harper's latest characterization lacked the nuance Baird offered just hours earlier in a call from Paris, where he was attending an international conference of diplomats from around the world gathered to plot strategy against ISIL.
The Paris conference was hosted by French President Francois Hollande and Iraqi President Fouad Massoum, whom Baird visited last week in Baghdad.
Baird travelled to Baghdad and the northern Iraqi capital of Irbil to deliver a message of tolerance and inclusion to a new Iraqi government that was sworn in last week. Dealing with the carnage being wrought by ISIL requires a multi-layered approach that's far from black and white, he said at the time.
"We are here to show our support for an inclusive government, the fight against terrorism, and to show support for a pluralistic Iraq, and to provide humanitarian assistance for the people who so desperately need it," Baird said at a news conference in Baghdad.
New Iraqi Prime Minister Haider al-Abadi last week succeeded Nouri al-Maliki, who was forced to step down after eight years.
Baird and many others have criticized al-Maliki for promoting a pro-Shiite agenda that alienated Iraq's Sunni minority — a disenfranchisement that many cite as one the so-called root causes for the rise of ISIL.
Baird said Monday that even though it is early days, he is seeing signs that al-Abadi is building a more inclusive government.
"I was pleased to hear the comments by the president and the new minister of foreign affairs. I was also struck by the spirit in the room, particularly from the Sunni Arab neighbours of Iraq who are hugely encouraged by what they're seeing coming out of Baghdad."
He said it was important for the new Iraqi government to win the "hearts and minds" of Sunnis and other minority groups. And he was unequivocal about the recent beheading of British aid worker David Haines, calling it a horrific atrocity.
Haines's videotaped murder at the hands of a masked ISIL killer with a British accent has heightened the sense of urgency for a co-ordinated international response to its threat. The militants have seized swaths of land across parts of Iraq and Syria.
"I think that there are people fighting from some 50 countries, likely from virtually every country from around the table this morning. Obviously we all want to do more," Baird said.
"For all of us, including my British counterpart, the fact that a development worker from the United Kingdom was most probably beheaded by another citizen of the United Kingdom was probably the most horrific thing we've learned in this battle."
Baird said Canada will conduct military airlifts out of the Czech Republic to supply Kurdish fighters in northern Iraq with arms and ammunition. Canada has also committed dozens of special forces troops to advise Iraqi troops.
Harper, who has said Canada won't send combat troops, used that pledge to dismiss opposition demands Monday for a full parliamentary debate.
House Speaker Andrew Scheer later granted a Liberal request for a debate on the Iraq deployment to take place Tuesday night.