If the reports are confirmed, Ukrainian separatists and their sponsors in Moscow will be responsible for a heinous crime: the destruction of a Malaysia Airlines passenger jet with 298 people aboard. The United States and its allies must insist that those responsible be held accountable — including those in the Kremlin.

The United States and its allies must not allow Russia and its agents to carry out a coverup. Instead, they should insist on an international investigation, sponsored by the U.N. Security Council, to determine how the plane was downed and where the weapon used against it originated. The Putin government should be challenged to support such an investigation or be seen by the world to block it.

At the same time, Western governments should stop allowing special interests and their excessive caution to impede robust sanctions against Russia for its behavior in Ukraine. To its credit, the Obama administration announced new sanctions Wednesday afternoon, the strongest yet taken. But the administration acted only after weeks of internal debate and negotiations with European governments that failed to produce comparable European Union action.

The White House continues to avoid measures that could inflict crushing damage on the Russian financial system and force Putin and the elites around him to choose between aggression in Ukraine and Russia’s economic future. Wednesday’s measures stop two banks from obtaining long-term debt financing in U.S. markets, but the treasury has not excluded those banks from the financial system nor taken measures against the largest banks. Though its bank was sanctioned, the energy operations of Gazprom, Russia’s giant, remain untouched.

Even before the tragic loss of the Malaysian plane, it ought to have been clear to the West that Russia’s aggression in Ukraine could not be overlooked or wished away. It is both criminal and intolerable and should be treated accordingly.