Ahead of his planned meeting this weekend with Russian President Vladimir Putin at the G20 summit in Australia, British Prime Minister David Cameron accused the Russian government of posing “great danger” to peace and stability in Europe, according to media reports. In a speech on Monday, Cameron reportedly said that Russia’s “illegal actions in Ukraine” are “destabilizing a sovereign state.”

“They (Russia) are ripping up the international rulebook and disregarding the democratic will of the Ukrainian people to determine their own future,” Cameron reportedly said, adding that the world should not forget the “consequences of turning a blind eye when big countries in Europe bully smaller countries.”

Cameron, referring to an earlier speech by former Soviet leader Mikhail Gorbachev, reportedly warning of a “new Cold War,” said that it is “not an outcome we believe to be inevitable.”

“But I will also be clear, that if Russia continues on its current path, then we will keep upping the pressure and Russia's relationship with the rest of the world will be radically different in the future,” he reportedly said.

He also defended the British government’s support for U.S.-backed economic sanctions on Russia, calling it not just “morally right” but also in the U.K.’s “national and economic interest.”

“There will be those who say that this isn't our business and that we shouldn't interfere. And some will argue that we can't -- that we have no influence to bear. But I believe both views are wrong,” he reportedly said. “Economic sanctions on Russia are having an impact. Capital has flown out of Russia, banks are short of finance, and the Russian stock market and rouble have fallen significantly.”

The U.S., U.K. and its allies have been up in arms against what they say is unprovoked Russian aggression in eastern Ukraine and Crimea. Russia has been accused of aiding pro-Moscow rebels in the region by sending troops and weapons.

Most recently, after Ukraine alleged last week that Russia was moving troops across its border into the rebel-held region of Luhansk, the Organization for Security and Cooperation in Europe reportedly confirmed that convoys of unmarked trucks and tanks had been seen entering the city of Donetsk.

However, Moscow has consistently denied that its troops are involved in the offensive against Ukrainian government forces, and has reportedly described Russian troops fighting alongside pro-Russian separatists as volunteers.