Defiant Russian president is the outsider at the G8 summit
Western leaders can no longer paper over differences with Russia, especially on Syria
Vladimir Putin's participation in the first G8 summit of his new term was supposed to seal his comeback to the global stage as Russia's paramount leader after winning a third presidential term last year.
Instead, it has brought to the forefront a Kremlin agenda increasingly at odds with Western values and raises fresh questions about Russia's membership in the club of the world's richest democracies.
On the first day of the summit in Northern Ireland, French President Francois Hollande reiterated the persisting disagreements with Russia over its close ally Syria.
US President Barack Obama's pledge to deepen co-operation with Putin after their talks could not mask a lack of major progress on any bilateral or international issues - or any personal warmth between the two leaders.
Canadian Prime Minister Stephen Harper might have captured the sour mood at the luxury Lough Erne resort when he said Putin did not belong in the G8 because he supported "the thugs of the Assad regime".
A member of the Russian delegation immediately dismissed the criticism as emotions that should not get in the way of major powers working together.
While Western leaders may no longer be willing to mask irreconcilable differences with Russia with smiles and back-slapping, Putin himself is increasingly prepared to set Russia against the West.
After talks with British Prime Minister David Cameron at Downing Street on Sunday, the Kremlin chief said it was incomprehensible how the West could support flesh-eating Syrian rebels, referring to widely circulated footage apparently showing a rebel cutting out and consuming the organs of a regime soldier.
Since the start of the war in 2011, Russia has supported the Damascus regime, its closest ally in the Middle East, while the West has backed the opposition.
Moscow said US intelligence claims that Assad had used chemical weapons were not persuasive and warned Washington against making the mistake it made when invading Iraq after claiming Saddam Hussein harboured weapons of mass destruction.
On the first day of the summit, Russia ramped up the confrontational rhetoric by saying it would not permit a no-fly zone to be enforced over Syria.
The West has occasionally voiced concern that Russia may not be worthy of a G8 seat ever since the country joined the group under then president Boris Yeltsin in 1997.
But the fresh doubts come as the Kremlin is overseeing an unprecedented crackdown on the opposition at home after Putin returned as president after four years as prime minister following a virulently anti-Western election campaign.
"The differences [between Russia and the West] are very serious," said Maria Lipman, an analyst at the Carnegie Moscow Centre. "I do not think the G8 will legally become a G7 but its influence will be waning, also because they don't speak with one voice."
Washington and Moscow seal cyberspace pact
The United States and Russia have signed an agreement to reduce the risk of conflict in cyberspace through real-time communications about incidents of national security concern.
The pact, the first of its kind, was announced in a statement by both countries at the G8 summit in Northern Ireland.
The agreement was cast as part of a broader bilateral effort to improve co-operation, including on counterterrorism and weapons of mass destruction.
The pact's components build on the US-Soviet experience in avoiding a nuclear war. A key element involves the US Nuclear Risk Reduction Centre, a round-the-clock centre built in 1987 so that Moscow and Washington could alert each other to missile tests that could be mistaken as acts of aggression.
The countries will use the centre to warn each other of cyber exercises that might be misperceived as attacks and as a channel to ask about incidents that raise national security concerns .
The agreement, two years in the making, also calls for a hotline, or secure phone link, so that the US cybersecurity co-ordinator and his or her Russian counterpart can speak directly in the event of a crisis.
Officials say privately they hope the new agreement can pave the way for similar pacts with other potential cyber foes such as China.
The Washington Post