(CNN) -- U.S. President Barack Obama had stern words for his Russian counterpart Vladimir Putin over Russia's actions in Ukraine, following a meeting Thursday of G7 leaders in Brussels, Belgium, at which Russia was excluded. Putin "has a chance to get back into a lane of international law," Obama said. But for this to happen, he said, Putin must take steps over the coming weeks that include recognizing Ukraine's new President-elect Petro Poroshenko, stopping the flow of weapons over the border into Ukraine and ceasing Russian support for pro-Russia separatists in Ukraine. "We cannot simply allow drift," Obama said, speaking alongside British Prime Minister David Cameron following bilateral talks.
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NEW: State media: Russia's ambassador will attend Poroshenko's inauguration
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Obama says Putin has a chance to "get back into a lane of international law"
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G7 leaders warn Russia they are ready to impose more sanctions over Ukraine
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Russia's Putin and Ukraine's new President-elect do not rule out meeting in France
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@placeholder may not have been at the table, but the summit's message was clearly directed at Russia.
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Putin may not have been at the table, but the summit's message was clearly directed at @placeholder.
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@placeholder also will be hosted by the French President on Thursday -- but at a separate dinner.
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Whether Putin and Poroshenko meet personally, Russia will give the new @placeholder president some official recognition when its ambassador to Ukraine attends Poroshenko's inauguration Saturday.