OTTAWA (AFP) - Canadian Prime Minister Stephen Harper called Russian aggression "the root of the ongoing conflict" in Ukraine on Thursday, after an airliner crashed in the country's strife-torn eastern region.

The Malaysia Airlines jet was carrying 298 people, including one Canadian. All were presumed dead.

"While we do not yet know who is responsible for this attack, we continue to condemn Russia's military aggression and illegal occupation of Ukraine," Harper said in a statement, adding that it was "at the root of the ongoing conflict in the region."

US and Ukrainian officials said the Boeing 777 jet was shot down by a surface-to-air-missile but could not say who launched the attack and from where.

Harper said he was "shocked and saddened" by the disaster, noting the presence of the Canadian national on board.

Canada has offered its assistance to authorities in determining the circumstances surrounding the crash of Flight MH17.