Tehran: The sacking of US national security adviser John Bolton was a “sign clear” that Washington’s campaign of sanctions against Tehran was failing, an aide to Iranian President Hassan Rouhani said. “Bolton’s marginalisation and his subsequent removal isn’t an accident but a clear sign of the defeat of America’s maximum pressure strategy” against Iran, Hesameddin Ashena tweeted. “Have no doubt that we have the power to manage the US approach towards Iran and will never back down. The blockade of Iran will break.” US President Donald Trump announced in a post on Twitter on Tuesday that he had asked Bolton to resign. Trump had a series of disagreements with the hawkish adviser, most notably on Iran which has been subject to crippling US sanctions since last year. The sanctions were imposed after Washington unilaterally withdrew from a 2015 deal that gave Iran relief from sanctions in return for curbs on its nuclear programme.