Tony Blair’s advisers privately questioned if the US had “proper political control” of military operations in Iraq after a senior US official confided that George W Bush believed he was on a “mission from God” against Iraqi insurgents, newly released documents reveal.

Blair needed to “deliver some difficult messages” to the then US president for a “more measured approach” in April 2004, following a US military operation to suppress a major uprising in the city of Falluja, according to papers released to the National Archives in Kew, west London.

In a surprisingly candid conversation, recorded in a document marked “please protect very carefully”, Richard “Rich” Armitage, then US deputy secretary of state, told Sir David Manning, then UK ambassador, that Bush had needed a “dose of reality” after demanding US forces “kick ass” in Falluja, where US troops were engaged in a bloody battle with Iraqi militants after four private military contractors were ambushed and killed.

Bush had initially been influenced by his military generals and “wanted to kick ass” with US marines occupying the city. But politicians on the coalition provisional authority, set up after Saddam’s fall, feared the US military response could damage hopes of establishing an independent Iraqi administration.

Bush backed off after being “faced with this ‘dose of reality’”, Manning reported back to No 10.