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abstract: 'We present 0.15-arcsec (1 kpc) resolution ALMA observations of the \[\] 157.74 $\mu$m line and rest-frame 160-$\mu$m continuum emission in two $z \sim 3$ dusty, star-forming galaxies - ALESS 49.1 and ALESS 57.1, combined with resolved CO(3–2) observations. In both sources, the \[\] surface brightness distribution is dominated by a compact core $\leq$1 kpc in radius, a factor of 2–3 smaller than the extent of the CO (3–2) emission. In ALESS 49.1, we find an additional extended (8-kpc radius), low surface-brightness \[\] component. Based on an analysis of mock ALMA observations, the \[\] and 160-$\mu$m continuum surface brightness distributions are inconsistent with a single-Gaussian surface brightness distribution with the same size as the CO(3–2) emission. The \[\] rotation curves flatten at $\simeq2$ kpc radius, suggesting the kinematics of the central regions are dominated by a baryonic disc. Both galaxies exhibit a strong \[\]/FIR deficit on 1-kpc scales, with FIR-surface-brightness to \[\]/FIR slope steeper than in local star-forming galaxies. A comparison of the \[\]/CO(3–2) observations with PDR models suggests a strong FUV radiation field ($G_0\sim10^4$) and high gas density ($n\mathrm{(H)}~\sim10^4-10^5$ cm$^{-3}$) in the central regions of ALESS 49.1 and 57.1. The most direct interpretation of the pronounced \[\]/FIR deficit 