Stephen Harper is the Prime Minister of Canada

The world is saddened and rightfully outraged by images of the charred remnants of Malaysia Airlines Flight MH17, and by the loss of almost 300 people from 11 countries, strewn across fields in eastern Ukraine. While the grim work of identifying victims' remains and tracking down the perpetrators of this appalling crime is just beginning, the world can be certain of one thing: There can be no weakening of our resolve to punish the Putin regime for threatening the peace and security of eastern and central Europe.

Although we may refer to militants in eastern Ukraine as "pro-Russian separatists," we are not confused by who, and what, they really are: an extension of the Russian state. They derive their material, political and logistical support from the Putin regime, and their criminal aggression and recklessness reflect the values of their Russian benefactors. Some have suggested that these agents of the Putin regime may have shot the plane down by accident. We do not, and may never, know. But accident or no accident, the blood is on the hands of the men who took such a risk and of the government that encouraged them to do so. Even if they did not intend to kill hundreds of innocent civilians, there is no denying their intent to continue waging a war on behalf of a regime that remains in violation of international law for its illegal occupation of Crimea.

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Russia's aggressive militarism and expansionism are a threat to more than just Ukraine; they are a threat to Europe, to the rule of law and to the values that bind Western nations. Canada will not stand idly by in the face of this threat.

That is why we have taken a strong stand, imposing a broad range of sanctions against those entities and individuals responsible for the ongoing crisis in Ukraine. Since the start of the crisis in Ukraine, Canada has imposed sanctions on nearly 150 individuals and entities. Earlier this week we broadened our approach, announcing economic sanctions against key sectors of the Russian economy.

It is why Canada has pledged more than $220-million in loan and loan guarantees which, once the appropriate conditions have been met to ensure that the funds are being used for their intended purposes, will help Ukraine to stabilize its economy and promote economic and social development. It is why we are providing training for the Ukrainian military, as well as Canadian military personnel and equipment to NATO's reassurance package in eastern and central Europe.

It is also why, last spring, G7 leaders decided to suspend preparations for the 2014 G8 Summit scheduled to take place in Sochi and convened instead as the G7 in Brussels. Through its actions, Russia under President Vladimir Putin has demonstrated that it does not share the values of this community of nations, dedicated as we are to democracy, international security, and the rule of law. Given this, it is difficult to foresee any circumstance under which Mr. Putin's Russia could be readmitted to the family of G7 nations.

Along with the sanctions imposed by our American and European allies, the measures undertaken by the international community are having an impact on the Russian economy. Investments are dropping and capital is leaving the country.

The steps Canada has taken have not been made without careful consideration of their potential impact on Canadian business interests abroad and at home. Like our allies, we will put our national interests first, but we will not allow business interests alone to dictate our foreign policy. With Mr. Putin's Russia increasingly autocratic at home and dangerously aggressive abroad, now is not the time to ease the diplomatic and economic pressure on the regime. Sustained, strong and co-ordinated action among like-minded countries is the best way to ensure that our actions have the maximum impact on the Putin regime.

Mr. Putin claims to abide by notions of stability, the rule of law and the peaceful settlement of international disputes, and yet we have seen reports this week of more Russian troops being moved to the border with Ukraine, while weapons and other supplies continue to flow freely over the border with his approval. It is time Mr. Putin matched his words with actions. He must reverse his course in Ukraine. He must withdraw his troops from the Ukrainian border, stop the flow of weapons and militants into Ukraine, and use his influence to persuade the militants, currently operating with the support of his regime, to lay down their weapons and cease the violence. He must also work to ensure that those investigating the shooting down of MH17 are not impeded in any way in their efforts to uncover the truth behind the deliberate or reckless targeting of innocent civilians.

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The choice is Mr. Putin's. He can take these actions to recommit Russia to peace, democracy, and the rule of law or he can persist with the politics of intimidation and aggression, in which case Canada – and its allies – must take further, more punitive steps to isolate Russia from the rest of the world's democratic states. The values and principles we cherish as Canadians, and for which so many generations have fought and died, demand it.