Britain and the United States are considering economic sanctions against Russia and Syria as there is no appetite among Western powers for a military solution to protect civilians from their bombardment in the civil war.
Foreign Secretary Boris Johnson, who spoke last week of the need to discuss “more kinetic options”, said military solutions such as a no-fly zone or no-bombing zone over Aleppo are “extremely difficult”.
Speaking after talks with US secretary of state John Kerry and other allies in London, Mr Johnson said Britain and its allies must work with the diplomatic “tools we have”.
He insisted that Russia was “feeling the pressure” from the international community over its military support of the Bashar Assad regime.
Alongside fresh sanctions, Mr Johnson said other measures such as threatening those responsible for committing war crimes with justice at the International Criminal Court “will eventually come to bite”.
Mr Johnson’s comments indicate his call to consider a potentially more forceful solution to stop the Russian and regime bombing of civilians in Aleppo does not command the support of Western allies.
Speaking after the four-hour meeting at Lancaster House, the Foreign Secretary said: “No option is in principle off the table but be in no doubt that these so-called military options are extremely difficult and there is, to put it mildly, a lack of political appetite in most European capitals and certainly in the West for that kind of solution at present.
“So we’ve got to work with the tools we have – the tools we have are diplomatic.
“I think the most powerful weapon we have at the moment is our ability to make president Putin and the Russians feel the consequences of what they are doing.”
Mr Johnson and Mr Kerry confirmed they were moving towards introducing fresh sanctions against “the Syrian regime and their supporters”.
The Foreign Secretary also described as “very significant” the French move to turn a visit from Vladimir Putin to Paris into a discussion about Syria, at which point the Russian president pulled out of the trip.
“They are starting to feel the pressure and it is vital that we keep that pressure up,” Mr Johnson said.
“There are a lot of measures that we are proposing to do with extra sanctions on the Syrian regime and their supporters, measures to bring those responsible for war crimes before the International Criminal Court.
“These things will eventually come to bite the perpetrators of these crimes and they should think about it now.”
Mr Kerry made it clear that US president Barack Obama has ruled nothing out but backed Mr Johnson’s assertion that support for military solutions is weak.
He said: “I don’t see the parliaments of European countries ready to declare war, I don’t see a lot of countries deciding that that’s the better solution here.
“So we are pursuing diplomacy because those are the tools that we have and we’re trying to find a way forward under those circumstances.
“It’s easy to say where’s the action, but what is the action?
“I have a lot of people who have a lot trouble defining that when they really get down to trying to do it.”
The pair called for a fresh ceasefire, just days after Mr Johnson said the US-Russia dialogue aimed at brokering a pause in hostilities appeared to have “run out of road”.
But after a meeting between Russian foreign minister Sergey Lavrov and Mr Kerry in Lausanne, Switzerland, on Saturday, Mr Johnson joined his US counterpart in calling for a truce.
The Foreign Secretary also insisted Russia and the Assad regime would not be successful in their “barbaric siege” of Aleppo, where 275,000 civilians are living under daily bombing raids, including alleged gas attacks and the use of highly destructive barrel bombs.
Stressing his belief that Russia and Assad were not capable of winning the war, he added: “So our challenge to the Russians is do the right thing by humanity.”
The Foreign Secretary said the talks, which included representatives from Germany, France, Italy, Turkey, Gulf and other Middle Eastern allies, focused on a range of proposals also including identifying al-Nusra terrorists in Aleppo which the regime and Russia are using as an alibi for their air strikes.
Mr Kerry said: “It could stop tomorrow morning, tonight if Russia and the Assad regime were to behave according to any norm or any standard of decency, but they’ve chosen not to.
“Instead we see what can only be described as crimes against humanity taking place on a daily basis, and hospitals are bombed and children are bombed or gassed.”