David Cameron has said that if it is proven that Ukrainian rebels did shoot down flight MH17, Russia would be to blame for having destabilised the country.
Hinting at further sanctions, the prime minister said Europe and the West must "turn this moment of outrage into a moment of action" and "fundamentally change our approach" to Russia.
"If it is the case, then we must be clear what it means: this is a direct result of Russia destabilising a sovereign state, violating its territorial integrity, backing thuggish militias, and training and arming them," Mr Cameron wrote in the Sunday Times.
"If president Putin does not change his approach on Ukraine, then Europe and the West must fundamentally change our approach to Russia.
Mr Cameron said it was time for Europe "to make our power, influence and resources count."
Thousands of online users have taken to social media to call for the victims of the Malaysian airliner crash to be returned to loved ones.
United States intelligence officials admitted that they do not know who fired the surface-to-air missile that downed flight MH17.
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