Russian President Vladimir Putin and Iranian President Ebrahim Raisi, at a summit in Samarkand in September.ALEXANDR DEMYANCHUK/SPUTNIK/AFP via Getty Images Iran has supported Russia by providing it with arms to use in Ukraine. That has worried the US, which sees it as part of a growing Russian-Iranian defense partnership. But there are signs that Moscow may not deliver on the agreements it has made with Tehran. Less than a year ago, the White House was warning of "unprecedented" military ties between Russia and Iran, but today, there are signs of increasing friction, with Moscow proving to be an unreliable partner.Late last year, as Russia risked depleting its missile stockpiles after months of fighting in Ukraine, Iran agreed to supply Moscow with arms, mostly Shahed-136 one-way attack drones, which Russia has used in attacks on Ukrainian cities and infrastructure.In December, National Security Council spokesman John Kirby said Iran and Russia were forging "a full-scale defense partnership" that would threaten the Middle East and the wider world.