Relations between Russia and the EU are stuck in a “deep and acute” crisis and are unlikely to improve until President Vladimir Putin leaves office and the conflict in Ukraine is resolved – events that could be many years away, the outgoing EU ambassador to Moscow has said.

Vygaudas Ušackas, who has been in the post since 2013, said the EU must offer Ukraine a path to membership of the bloc if it wants to resist Russian attempts to bring the former Soviet state more firmly back under Moscow’s control.

“As I leave my post, I am pessimistic that we will be able to return to a normal partnership in the near future,” Ušackas wrote in a letter published in the Observer on Sunday. “The differences between us are vast and hinge on principles of European security.”

He detailed growing attacks on “core European values” of democracy, free speech and the rule of law and said the apparatus of the Kremlin apparatus is focused on returning Putin to power in 2018 elections that it can present as “smooth and credible”.

“Over the course of a six-year presidential term that will follow, it seems probable that the current clash of world views between Moscow and the west will continue,” he said, adding that Russia will attempt to exploit divisions inside Europe to undermine it.

Efforts to influence elections and politics through propaganda are well-documented, but Moscow is also using business deals to try to splinter the bloc by rewarding countries that challenge sanctions and the broader EU position on Russia, he said.

“In unity lies our strength. It is precisely our internal problems that Moscow is exploiting to undermine the credibility of the EU model,” he said.

Member states are not doing enough to protect themselves, he said, noting the new North Stream II gas pipeline, a project which, he said, hands Moscow more control over Europe’s energy, in direct opposition to Europe’s goals of diversifying suppliers.

Vygaudas Ušackas, outgoing EU envoy to Moscow. Photograph: Kommersant Photo/Getty Images

Europe must focus on managing Brexit and the refugee crisis, both of which have been exploited by Russia, improve transparency to build the trust of citizens around Europe, and focus on remaining united.

European leaders must also stand up for rights which are under attack in Russia. “As Soviet dissident and leading human rights champion Lyudmila Alexeyeva reminded me recently: ‘Please tell Brussels not to give up on the Russian people,’” he said.

Ušackas expects Moscow to push for greater control over Ukraine and Georgia. “Russia respects the sovereignty and territorial integrity of its neighbours only as long as their geopolitical choices align with Moscow’s interests,” he said.

The EU needs to step up efforts to negotiate peace in Ukraine, he said, calling on Brussels to name a special envoy to the country, a position the US has already created, and questioned why the EU was not part of current multilateral efforts to broker an agreement.

“We need a greater focus on ending the Ukrainian conflict, because it will be difficult to normalise relations while it continues,” he said.

That should include offering Ukraine a path to EU membership. The prospect of EU membership would send Russia a clear message about commitment to Ukrainian and Georgian democracy, and give the governments motivation to make important reforms.

“It must be made very clear: the road to Europe goes via Kiev, with respect of Ukraine’s European choice, and adherence to the European security order. It cannot go through ‘managed’ democracy in Russia itself.”