President Vladimir Putin on Wednesday warned the United States and its allies against launching a unilateral military strike against Damascus, saying the West’s case against Syrian President Bashar al-Assad doesn’t stand up to scrutiny.

In an interview published Wednesday by the Associated Press, Putin said Russia is developing a plan of action in case the United States does attack Syria without United Nations approval, but he declined to go into specifics.

He said Russia — Syria’s most stalwart ally — has frozen the shipment of certain parts for S-300 anti-aircraft missiles that it had agreed to sell to Assad’s regime.

Putin said that if the United States and its allies could provide sufficient evidence that Assad’s forces carried out a chemical weapons attack on Aug. 21 in a Damascus suburb, Russia would consider allowing United Nations action against Syria.

U.S. Secretary of State John F. Kerry said Friday that U.S. intelligence agencies have “high confidence” that Assad’s government was responsible for the attack, based partly on knowledge of regime officials’ conversations about it and the tracking of movements of regime personnel before and after the strike.

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But Putin told the Associated Press that he remains skeptical, in part because it seems unlikely that Assad would risk international repercussion by using long-banned chemical weapons to kill hundreds of men, women and children.

“It ought to be convincing,” Putin said. “It shouldn’t be based on some rumors and information obtained by the special services through some kind of eavesdropping, some conversations and things like that.”

Russia has blocked U.S. and British efforts to have the U.N. Security Council take action against Syria for the attack. British Prime Minister David Cameron backed off efforts to join the United States in possible missile strikes after encountering strong resistance at home. In France, however, Foreign Minister Laurent Fabius said his country is prepared to act in conjunction with the United States.

If the United States decided against military involvement, “this type of action wouldn’t be possible, and so we would have to consider the Syrian question in another way,” Fabius said in an interview with France Info Radio on Wednesday, hours ahead of a scheduled debate in parliament about France’s potential involvement in Syria.

President Francois Hollande does not need consent from lawmakers to order military action. But opinion polls in recent days suggest that a move against Syria is unpopular among the French public.

Fabius said it was “possible” that Hollande, whose party has a strong majority in parliament, would hold some sort of vote about whether to act. But he said that nothing would be done until “the president has all the elements in his hands.”

The global response to Syria is bound to be a major topic as the leaders of the Group of 20 countries gather outside St. Petersburg for a summit Thursday and Friday, even though the meeting is supposed to be about economic growth.

Putin and President Obama are not scheduled to meet one-on-one. Obama considered coming to Moscow ahead of time for a direct meeting with Putin but opted not to, amid rising tensions over Syria, confidential files leaker Edward Snowden and other issues. So Putin invited the Associated Press to sit down with him instead.

The lengthy interview took place at his country residence late Tuesday night, with both the Associated Press and Russian television’s First Channel in attendance. Putin touched on his country’s relations with the United States, his sometimes “vexed” but generally constructive relations with Obama, and a host of other topics — including Syria, Snowden, gay rights and Moscow mayoral candidate Alexei Navalny.

“This man brings problems wherever he appears,” Putin said of Navalny, Russia’s most famous anti-corruption campaigner. Navalny, who memorably labeled Putin’s United Russia the “party of crooks and thieves,” is currently appealing a six-year sentence for extortion on charges that he claims were trumped up at the Kremlin’s behest.

Despite a new law prohibiting “propaganda” that promotes homosexuality, Putin denied that Russia is anti-gay. He said Obama is welcome to meet with lesbian, gay, bisexual and transgender activists while he is in St. Petersburg for the G-20 meeting and mentioned that he would be willing to meet with such activists himself if they are interested.

One of Russia’s most prominent defenders of gay rights, Nikolai Alekseyev, tweeted on Wednesday that he would be glad to take up Putin’s offer.

On Snowden, the spiller of National Security Agency secrets who fled to Moscow, Putin confirmed that Russian officials had been in touch with him while he was still in Hong Kong.

The interview took place in a cream-colored drawing room in Putin’s residence at Novo-Ogaryovo. He came across as relaxed but engaged, occasionally making a fist to emphasize a point. He didn’t pick any fights with the United States, suggesting instead that Moscow and Washington generally get along fairly well on a range of issues.

“President Obama hasn’t been elected by the American people in order to be pleasant to Russia,” he said. “And your humble servant hasn’t been elected by the people of Russia to be pleasant to someone either.”

About Obama, he said, “We work, we argue about some issues. We are human. Sometimes one of us gets vexed. But I would like to repeat once again that global mutual interests form a good basis for finding a joint solution to our problems.”

On Syria, Putin emphasized the points that he and other Russian officials have made previously: He said it would have been “ludicrous” for Assad’s forces to use chemical weapons, when the whole world was watching and they were gaining the upper hand against the rebels.

Michael Birnbaum contributed to this report from Paris.