The UK foreign secretary, Philip Hammond, has warned Russia that its military intervention in support of the Assad regime could mean Moscow shares criminal responsibility for the regime’s use of barrel bombs against its own people.

Hammond was speaking minutes before the start of a UN security council session called by Moscow on a morning in which Russia carried out its first bombing sorties inside Syria. The foreign secretary said that Britain was still trying to confirm the targets of the airstrikes but added: “If they’re in an area where there’s no Isil [an acronym for Islamic State, also known as Isis], it will send a very clear message that the intervention is there to support Assad.”

Early reports suggested that the Russian airstrikes may have struck non-Isis rebel groups, including those supported by the west.



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The airstrikes, said Hammond, changed Russia’s legal position as a party to the conflict.

“Now the Russians are now very openly and ostentatiously there propping up the regime, they are vulnerable to international pressure,” he told a group of journalists. “They have a shared responsibility. They may arguably have a legal exposure to this barrel bombing activity. Barrel bombing is criminal. It breaches international humanitarian law.”

The US secretary of state, John Kerry, said on Tuesday the US was seeking to persuade the Russians and the Iranians to use their influence on the Assad regime to stop using barrel bombs. Hammond said Vladimir Putin’s military gambit in Syria increased his leverage and his responsibilities. If he wanted Russia to be part of a wider coalition, he should “build confidence” in his intentions by focusing on attacking Isis and persuading the regime to curb its “worst excesses”, Hammond said.



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“The argument to Putin would be that even in his own terms, it makes sense,” the foreign secretary said. “He is going to be associated with this regime and he surely doesn’t want to be associated with a regime that is carrying out barrel bombing and chlorine attacks on his own population. At least stop that from happening. Use your leverage.”

At the security council, Lavrov said that Russia would present a resolution providing a mandate for an international military campaign against Isis, based on international law. He made clear that such a campaign would only be legal if it was carried out in partnership with the Assad regime. Hammond said that on that basis, there would be no agreement on the resolution.

“I would be astonished if anything came out of the meeting,” Hammond said. “I don’t think the security council will be willing to say anything that doesn’t involve a reference to Assad ultimately not being part of the new Syria, and I don’t see the Russians at this stage being able to accept that kind of language.”

In his address to the security council meeting, the French foreign minister, Laurent Fabius, said that his country’s support for a coalition including Russia was dependent on three conditions: that it was focused on attacking Isis exclusively; that there was an end to regime barrel bombing; and that there was a political transition so that “the fate of the people can not be to choose between two types of horror, terrorism and the regime”.

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Fabius’s Chinese counterpart, Wang Yi, called for a third Geneva conference on Syria “without preconditions” – a reference to western insistence the ultimate outcome of talks would be a transition in which Assad steps down.

Hammond said that the UK would support a transition in which it was stipulated that Assad, even if he did not step down on “day one”, would not stand in any future elections.



“We’d want to absolutely explore with them [the Russians and Iranians] what the transition mechanisms would look like, at what point in the transition Assad would go. The key thing for us would be clarity that when we get to elections, Assad will not be a candidate in those elections,” Hammond said.

He said that he had talked to the Iranians over Assad’s future. He found that although they had different interests in Syria, they were just as firmly committed to the regime.

“Iran has a different position from the Russians. Whether that makes them more flexible, I have my doubts,” he said. “Iran has different equities they are protecting, of course. To Iran, Syria is many things, but one of them is a supply line to Hezbollah in Lebanon, and I have difficulty myself envisaging a scenario in which Iran would willingly consent to a solution in Syria that would cut its supply line to Hezbollah.”