Two Canadians are among the 62 confirmed fatalities in the Nairobi raid and hostage-taking by the Somalia-based, al-Qaida-linked group al-Shabab. More than 175 people were injured in the assault that began Saturday and remained unresolved Monday afternoon.
An early, unconfirmed report linked to al-Shabab claimed a Canadian was among the "mujahedeen" who staged the attack.
The prime minister, at a press conference with his visiting Italian counterpart Enrico Letta, refused to comment directly, saying he never discusses national security operations.
"We obviously monitor developments very closely," said Harper. "We exchange information on the travel and activities of persons of interest all around the world."
Indeed, Monday was a busy day in Canada on the terrorism front.
Federal lawyers were in an Edmonton courtroom arguing against Omar Khadr being moved from a maximum security federal penitentiary to a provincial jail. The 27-year-old Canadian spent years imprisoned at Guantanamo Bay before pleading guilty to terrorism charges in a U.S. military court in 2010.
And in Toronto, federal prosecutors bypassed a preliminary hearing and sent two men directly to trial for an alleged terror plot against a Via Rail train.
Canadians have also been implicated in last January's deadly Algerian gas plant attack, and a Canadian has been named by Bulgarian officials as a suspect in last year's bus bombing in Burgas.
Harper, however, waved off any suggestion that a pattern is emerging.
"I don't obviously discuss, in any detail, security operations," Harper said.
"I'm not worried about such a thing as a mass phenomenon, but obviously there are always cases that we follow very closely and work with our international partners on."
Following up in French, the prime minister was more explicit, saying "this is not a phenomenon that is based only in one country. It exists across the globe."
"Is there a significant phenomenon of radicalization here? I don't think so," Harper said. "But obviously our security agencies are always paying great attention to individual cases and they're working closely with our international partners."
Diplomat Annemarie Desloges was one of two Canadians killed when gunmen stormed Nairobi's upscale Westgate mall, firing AK-47s and lobbing grenades inside a lavish shopping venue frequented by expatriates and wealthy locals.
Media reports and Facebook users identified Vancouver businessman Naguib Damji as the other Canadian victim.
Canadian officials have also said at least two Canadian citizens were among the 175 injured.
Hodan Hassan told The Associated Press that her Canadian nieces, Fardosa Abdi, 17, and Dheman Abdi, 16, were shopping when the siege began.
Fardosa is in critical condition after undergoing two surgeries for severe leg injuries, according to her aunt, while Dheman had a bullet break her leg and an explosion injure her arm.
Late Monday, Kenyan security forces were in the final stages of flushing out the attackers. The country's interior minister said it was unlikely that any more hostages remained inside Westgate Mall.
Three attackers were killed in the fighting Monday, officials said, and more than 10 suspects arrested. Eleven Kenyan soldiers were wounded in running gun battles. By evening, Kenyan security officials were claiming the upper hand.
For the second time in as many days, Harper extended his condolences to the families, friends and colleagues of the victims in Nairobi.
And he issued a stern rebuke to the Canadian supporters of Khadr, whose court date in Edmonton marked his first public appearance in 11 years.
Khadr was 15 when he was shot and captured by American soldiers in Afghanistan. In 2010, he pleaded guilty to war crimes before a U.S. military commission and was sentenced to eight years. He was transferred to Canada last fall.
"This is an individual who pled guilty and was convicted of very serious crimes, including murder, and it is very important that we continue to vigorously defend against any attempts in court to lessen his punishment for these heinous acts," Harper said.
"We will continue to do everything in our power to empower our police and security forces to deal with threats, and to work with the international community in identifying these because they are inevitably cross-border in nature."
— With files from The Associated Press
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