To improve the NO modelling in turbulent flames, the flamelet/progress variable (FPV) model is extended by introducing NO mass fraction into the progress variable and incorporating an additional NO transport equation. Two sets of flamelet databases are tabulated with progress variables based on major species and NO mass fraction, respectively. The former is used for the acquisition of the main thermochemical variables, while the latter is employed for NO modelling. Moreover, an additional transport equation is solved to obtain the NO mass fraction, with the source term corrected using the scale similarity method. Model assessments are first conducted on laminar counterflow diffusion flames to identify lookup-related errors and assess the suitability of progress variable definitions. The results show that the progress variables based on major species and NO could correctly describe the main thermochemical quantities and NO-related variables, respectively. Subsequently, the model is applied to the large eddy simulation (LES) of Sandia flames. The results indicate that the extended FPV model improves the NO prediction, with a mean error for NO prediction at 55%, significantly lower than those of existing FPV models (130% and 385%). The LES with the extended FPV model quantitatively captures NO suppression in the mid-range of Reynolds numbers from 22 400 (Flame D) to 33 600 (Flame E), but underestimates the NO suppression at higher Reynolds numbers from 33 600 to 44 800 (Flame F). This underprediction is primarily attributed to the underestimation of local extinction levels in flames with high Reynolds numbers.