Russia seemingly has ignored Secretary of State John Kerry’s appeals to stop bombing civilians and allow critical humanitarian aid to starving Syrians – and is instead escalating its military involvement, deploying four of its most capable fighter jets to Syria, two defense officials confirmed to Fox News.

The decision to send the Su-35S jets poses yet another hurdle for Kerry’s efforts to proceed with peace talks. The Su-35S is Russia’s most advanced warplane, capable of air-to-air and air-to-ground missions, one official familiar with the jet said.

Already, continued Russian airstrikes against Syrian opposition fighters, some backed by the CIA, were enough to derail proposed peace talks in Geneva Wednesday.

Despite backing two U.N. resolutions in support of a ceasefire, Russia reneged on its promise to stop bombing civilians in Syria, a prerequisite for the U.N.-backed talks in Geneva.