The former Polish Prime Minister was speaking on the third anniversary of the downing of Malaysian Airlines flight MH17 over Ukraine which resulted in the loss of almost 300 lives.
A Dutch-led investigation has concluded that the missile that downed MH17 was fired from rebel-held territory in eastern Ukraine from a launcher that had crossed the border from Russia.
The Russians insist the Ukrainian military downed the aircraft.
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Investigators last year said they had pinpointed 100 people they want to speak to who are believed to have been involved in transporting the missile launcher or its use.
Nations involved in the investigation have agreed to prosecute any suspects in the Netherlands, home to nearly 200 of the victims. EU foreign affairs chief Federica Mogherini has called for international cooperation in the hunt for the perpetrators.
Tusk said, "The EU has again made clear that we stand steadfastly behind Ukraine against Russia's aggression and attempts to subvert your independence. We reiterated our continued support for Ukraine's territorial integrity and sovereignty."
He added, "We do not recognise the illegal annexation of Crimea. We call for the full implementation of the Minsk agreements by all sides, underlining Russia's responsibility in this regard. On 28 June, the EU again decided to roll over its economic sanctions against Russia."
Tusk was speaking after the EU recently finalised the ratification of the EU-Ukraine association agreement, which will enter into force on 1 September.
On this, he said, "The provisional application of the trade part that entered into force last year has already increased our trade by 25 per cent. The fully ratified agreement will allow us to further strengthen our cooperation and to deepen the political association and economic integration of Ukraine with the EU."
Tusk told Ukrainian President Petro Poroshenko, "We have achieved a lot, but we are still only halfway down the road. I am convinced that if you continue to be as determined, as courageous and as consistent as you were back then in Maidan, as you were during the struggle for Ukraine's integrity, if you can withstand the burden of reforms and not give up, then you will reach your dreams and goals."
Meanwhile, speaking on Monday, Pavlo Klimkin, Ukraine's foreign minister, said, "Three years ago a world becoming accustomed to the most despicable terrorist outrages was shocked and stunned when 298 passengers and crew members of the Malaysian Airlines flight MH17 were blasted out of the skies over Ukraine.
"For many around the world it brought the Russian fomented war in Donbas to their attention for the first time. Even for Ukrainians, including those facing death in Donbas, it was impossible to believe that terrorists had the ability to hit the civilian aircraft 11,000 meters above the ground. Even with all the support Russia was known to be providing it was simply not credible or believable in any way.
"Can economic and political sanctions or awards in criminal case compensate the grief of so many who lost their loved ones? No, I am afraid it cannot. But the Ukrainian government has made a pledge - and we are determined to do everything in our power to unveil the truth and bring those responsible for this mass murder to justice."