The steady advance of Russian tanks, artillery and troops into the rebel-held Donbas region of eastern Ukraine, documented last week by Nato and independent international observers, is an alarming reminder that the crisis that followed last March’s annexation of Crimea is far from over. As was the case in August, when the arrival of Russian reinforcements presaged renewed fighting between the all-but-defeated separatists and government forces, Moscow flatly denies involvement. If Russian soldiers are present in the Donetsk and Luhansk oblasts, it must be because they are there on holiday, the Kremlin suggests. Such risible mendacity is a measure of the vast contempt in which Russia’s president, Vladimir Putin, holds last September’s Minsk ceasefire agreement, the democratically elected government in Kiev and the international community as a whole.

As ever, Russia’s intentions in Ukraine are unclear. The troop movements, possibly including Chechen and Cossack mercenaries, may simply be an attempt to bolster the separatists who do not have the numbers or the weaponry to resist Kiev’s will indefinitely. Or they may be part of a wider effort to underpin the independence of the Donbas, following recent separatist victories in rigged elections that all but Moscow deemed illegitimate. Some analysts fear Putin, pursuing his dangerous fantasy of a restored Russian imperium, harbours longer-term plans to turn eastern Ukraine into a permanent, militarised bridgehead or statelet – a sort of modern Sparta – from which to project an ongoing campaign of destabilisation against Ukraine and its pro-western leadership.

Whatever he is up to, the fact that all this was happening at the very moment when Putin was meeting Barack Obama, David Cameron and other world leaders at this weekend’s G20 summit in Brisbane is little short of incredible. Since Putin began illegally seizing Ukrainian territory, the international community has imposed extensive sanctions in a bid to stop him. But numerous attempts to engage him diplomatically and personally, not least by Obama and Germany’s chancellor, Angela Merkel, have all failed miserably. Putin’s rejection of such entreaties, fortified by his perception of western weakness, his grievances with the US, and his apparently immeasurable contempt for his critics, seems invincible. To his credit, Cameron did not mince words during “robust” bilateral talks with Putin. His message that there cannot be business as usual as long as Russia’s Ukraine intervention continues is wholly right. Putin appeared in no mood to listen. But his decision to leave the summit early, while suggesting continuing recalcitrance, may also reflect his surprise, even shock, at the fierce criticism directed at him there. This might just have some beneficial effect in the longer run.

It is not just Ukraine. The pattern of accelerating Russian confrontationalism abroad and authoritarianism at home, evident since Putin first took power as prime minister in 1999, is unmistakable. As a report published last week by the European Leadership Network demonstrated, close military encounters between Russia and the west are now back at cold war levels, with all the associated dangers that entails. Russia has resumed long-range patrols by nuclear-capable bombers, discontinued in 1992, to destinations as distant and provocative as the Gulf of Mexico. Russian warships showed up last week in international waters off Australia, crudely advertising Putin’s arrival in Brisbane.

Avid for its resources and oblivious to the environmental consequences, Moscow plans new military bases and operations across the Arctic. Meanwhile, figures as diverse as Mikhail Gorbachev, the former Soviet leader, and Sauli Niinistö, Finland’s president, have warned that the world is on the brink of a new cold war. In the Baltic republics of Estonia, Latvia and Lithuania, across eastern Europe, in Georgia and Moldova and throughout Scandinavia, concern is rising about renewed Russian aggression amid a flurry of maritime and airspace violations.

Putin’s disregard for international norms is mirrored at home by his disrespect for individual human and civil rights. Russia under Putin is a country where the rule of law and property rights are not guaranteed, where the police and judiciary lack independence, where the legislative process is wholly dominated by the executive, where the media and civil rights groups are co-opted or persecuted, and where brave individuals such as the Pussy Riot punk group or the investigative journalist Anna Politkovskaya pay a terrible price for their defiance.

At least the Soviet Union had a distinct ideology based on ideals, however deluded they proved to be. Putin’s only principle seems to be national and personal aggrandisement. “We in the west need to reassess our relations with Russia,” says Finland’s prime minister, Alexander Stubb. “We have put in a lot of effort to try to integrate Russia into western institutions and we slightly idealistically believed that Russia could become a normal, liberal market democracy that relies on international institutions. It hasn’t.”

It is difficult to justify Putin’s invitation to Brisbane, and other international forums such as last week’s Apec summit in Beijing. It requires a pretence that his repeat acts of geopolitical hooliganism are somehow tolerable. They are not and he is not welcome (as the G7 grouping has previously ruled). Putin surely has no place in the high councils of an international system whose rules and values he so blatantly subverts. In short, it is time to end wishful thinking about a change of heart in Moscow, to stop pulling punches and to let Putin know that until Russia accepts the inviolable sovereignty of international law and the moral imperative of universal human rights, it will be an outcast among nations.

The means of bringing Putin to heel, in Ukraine and elsewhere, are available. Russia’s economy has been badly hit by sanctions, but their indirect effect has been even greater. Foreign investment has slumped as confidence crumbles. Russia’s central bank recently downgraded its growth forecasts again and said capital flight was approaching record levels. Russia’s currency, the rouble, has lost almost 30% of its value this year, prompting sharp price rises. Despite new oil and gas export deals with China, the regime is running on empty as international oil prices drop. And polls suggest most Russians do not believe Ukraine is worth fighting for.

Putin is vulnerable. Increased financial pressure coupled with intensified diplomatic action and bolstered Nato support for European countries bordering Russia could convince Moscow that the costs of its antisocial behaviour are too high to bear. As for Putin, world leaders should stop treating him as if he were somehow one of them. Putin and Putinism are a throwback to a more polarised and aggressive era. He must not be allowed to drag the world back to the past.