World music may have colonised Radio 3, but despite its avowed radicalism (and Paul Simon's best efforts) rock has proved largely resistant to its varied influences. Which makes Nina Nastasia's current tour, in which the US singer is joined by two musicians from Tuva (next to Mongolia) heartening indeed.

Then again, Nastasia hardly makes conventional pop. Her three albums, recorded by Nirvana producer Steve Albini and praised to the rafters by John Peel, are musically spare and emotionally intense affairs with a heavy country influence. Tonight, she stands centre-stage, her hair tightly bundled and her hips swaying slightly, presiding over an impressively rapt audience. When, three songs in, drummer Jim White finally swaps his brushes for sticks and kicks his kit into life, it feels like a glacier has broken.

It's an absorbing spectacle, with Nastasia's insistent guitar lines and tales of obsession, inertia and heartbreak underpinned and disrupted by a fine backing band that includes Joshua Carlebach on accordion and Dylan Willemsa on viola.

Multi-instrumentalists Kaigal-ool Khovalyg and Sayan Bapa arrive after the break, and turn out to be two short men in black with moustaches, equipped with igils (horse-hair cellos) and doshpuluurs (long-necked lutes). Their presence is not always as significant as you might expect - many of Nastasia's arrangements remain unchanged, and often they act like an unobtrusive string section.

At times, though, the cumulative effect is staggering: Khovalyg and Bapa are experienced throat-singers and, while Nastasia sings of easy chairs and freeways, their voices lift and dive from eerie whine to reedy burr. It's a thrilling moment, and one whose incongruity is only fleeting: traditions meet, and are melded.

Nastasia ends the gig, alone, with an encore whose high point is Rosemary, an achingly bare tale of love and loss. You can almost feel the lump rising in the audience's collective throat, before she backs off from the mic and exits without a backward glance.

· At St George's, Bristol (0117-923 0359), tonight, then touring.