LONDON — UK Prime Minister Theresa May has mounted a stern attack on Russia, claiming that it interferes in elections and plants fake news stories to sow discord and undermine Western institutions.

In a significant escalation of rhetoric, May accused Moscow of attempting to “weaponize information” as part of a “sustained campaign of cyberespionage and disruption.” Russia’s actions were “threatening the international order,” she said.

“We know what you are doing. And you will not succeed. Because you underestimate the resilience of our democracies, the enduring attraction of free and open societies, and the commitment of Western nations to the alliances that bind us,” May said in a speech at the annual Lord Mayor’s Banquet in London on Monday.

Since its annexation of Crimea, May said Russia had fomented conflict in eastern Ukraine, violated airspace of European countries, and hacked the Danish ministry of defense and the German Parliament.

May said Britain would act to defend itself. “The UK will do what is necessary to protect ourselves, and work with our allies to do likewise,” she said. “So we will take the necessary actions to counter Russian activity. But this is not where we want to be — and not the relationship with Russia we want.”

Her criticism comes amid mounting allegations that groups linked to Russia or the Kremlin itself meddled in elections and referendums, including Brexit, Catalonia’s independence vote, and the 2016 US presidential election.

Senior Russian officials reacted angrily to May’s comments.

“The world order that suits May, with the capture of Iraq, war in Libya, creation of [ISIS], and terrorism in Europe, has outlived itself. It can’t be saved with an attack on Russia,” tweeted Alexey Pushkov, a Russian lawmaker who is also head of the Federation Council Committee on Information Policy. He also accused the British media of peddling “fake news” on issues such as the Iraq war and Syria.

Konstantin Kosachev, Head of the Federation Council Committee on Foreign Affairs, said in a Facebook post Tuesday that May’s speech was “surprisingly full of ideological cliches.”

“The mistake is that this conflict is not ideological and there will be no “triumph of Western values” this time, no one is fighting them here,” he wrote. “However, to force the West to behave in a democratic and not in an authoritarian way on the international arena is not only Russia’s desire, it’s the desire of the whole world. And this cannot be ignored.”

May’s comments contrast starkly with US President Donald Trump’s recent comment that he believed Vladimir Putin’s denials of interfering in the 2016 US presidential elections.

The UK Prime Minister said that even as the United Kingdom leaves the European Union, it remains committed to maintaining Europe’s security through strong economic ties with allies and NATO. Such relationships will protect against security threats from Russia, she said.

“That is why we are driving reform of NATO, so this vital alliance is better able to deter and counter hostile Russian activity. It is why we have stepped up our military and economic support to Ukraine. It is why we are strengthening our cybersecurity and looking at how we tighten our financial regimes to ensure the profits of corruption cannot flow from Russia into the UK,” she said.

She cited Russian President Vladimir Putin’s recent comment that “when a state fails to observe universal rules of conduct and pursues its interests at any cost, it will provoke resistance and disputes will become unpredictable and dangerous.”

“I say to President Putin, I agree. But it is Russia’s actions which threaten the international order on which we all depend,” she said. “We do not want to return to the Cold War, or to be in a state of perpetual confrontation.”

International order faces other threats from regions where “the absence of strong states” has created instability and conflict, such as the Middle East.

“We see the spillover effects of this instability in the challenge of mass migration and humanitarian crises in countries like Yemen,” she said.

She urged European and American allies to join the UK in stepping up efforts to contain and solve conflicts. She called attention to Yemen, Libya and Iraq and called for continued work toward a two-state solution in the Middle East peace process.

“As part of this, while we will stand firm in our support for the Iran nuclear deal, we are also determined to counter destabilizing Iranian actions in the region and their ballistic missile proliferation, working with the US, France and Germany in particular,” she said.

“It is in all of our interests to get this right: to bring long-sought stability to the Middle East, ensure these growing economies can play their full role in the global system, and reinforce a rules-based international order.”

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