Ahead of talks between Boris Johnson, US Secretary of State John Kerry and other Western powers, Andrew Mitchell said civilians must be shielded from Russian and Syrian regime bombing.
Mr Mitchell said the West should look at enforcing both a no-fly zone, which could involve confronting Russian jets that violate it, and a no bombing zone, which could see retaliatory responses to attacks on civilians.
According to reports, Mr Johnson is more open to the idea of a no bombing zone, in which the West would respond to attacks on civilians in designated safe havens by bombing Syrian military installations.
Mr Mitchell told ITV’s Peston on Sunday: “I think that we should be looking at both enforcing a no-fly zone and a no bombing zone, they are different of course.”
He claimed a no fly zone would “not necessarily” mean shooting down Russian jets, saying “it means that we take a stand” and insisting there are “other mechanisms” of policing it.
“I believe that the world decided that we would defend innocent people, we had a responsibility to protect hammered out at the United Nations, agreed by all the world powers and that we have a duty and a responsibility to the 250,000 people who today are left alive in Aleppo, of whom 100,000 are children, we have a responsibility to protect them,” he said.
“I think the international community should be absolutely clear about that.
“There is no question we have the ability and the power to enforce a no-fly zone, a no bombing zone, the issue is the political will.
“Unless we didn’t mean it when we said no more Rwanda, no more Srebrenica, no more Bosnia, unless we were just using political words, we have to stand by what we promised.”
Mr Mitchell added: “Of course no one wants a war with Russia or to be shooting down planes and so forth, but we should be clear that we will not allow Russian military might to used to attack innocent civilians.
“That is what they are doing, they are not attacking military formations in Aleppo, they are attacking children and their parents hiding in their cellars in the rubble and they are attacking hospitals, that is a war crime.”
The Foreign Secretary’s talks with Mr Kerry today are expected to consider “all options” for ending the bloodshed in Syria after fresh discussions between the United States and Russia ended without a solution.
On Saturday, Mr Kerry met Russian Foreign Minister Sergei Lavrov and envoys from the major Middle Eastern players in the civil war for talks in Lausanne, Switzerland, which lasted four and a half hours.
Mr Kerry said the discussions focused on “trying to find something that works other than military action” and that minsters offered suggestions that “really might be able to shape some different approaches”, although no concrete steps were taken.
Mr Johnson has said it is time to consider “more kinetic options” including “military options” as Syrian regime forces and their Russian backers continue to pound rebel-held areas of Aleppo.
President Bashar Assad has said he wants to recapture the northern city’s rebel-held eastern areas to provide the regime with a “springboard” with which to retake other areas of the country.
On Thursday, Mr Johnson said the US-Russia dialogue aimed at brokering a ceasefire appeared to have “run out of road” and there was a need to find an alternative way forward.
His comments followed cross-party calls from MPs for the establishment of a no-fly zone to end the air strikes on Aleppo, although the foreign secretary said they had to be “realistic” about what could be done.
With time running out for the Obama administration and the US in the grip of an extraordinarily bitter presidential election, he acknowledged it may be some time before Washington was ready for a new initiative.
Representatives from Germany, France and Italy will also attend Sunday’s summit in London, aiming to reduce the violence and improve humanitarian access.