  A search for massive coloured resonances which are pair-produced and decay
into two jets is presented. The analysis uses 36.7 fb$^{-1}$ of $\sqrt{s}=$ 13
TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and
2016. No significant deviation from the background prediction is observed.
Results are interpreted in a SUSY simplified model where the lightest
supersymmetric particle is the top squark, $\tilde{t}$, which decays promptly
into two quarks through $R$-parity-violating couplings. Top squarks with masses
in the range 100 GeV < $m_{\tilde{t}}$ < 410 GeV are excluded at 95% confidence
level. If the decay is into a $b$-quark and a light quark, a dedicated
selection requiring two $b$-tags is used to exclude masses in the ranges 100
GeV < $m_{\tilde{t}}$ < 470 GeV and 480 GeV < $m_{\tilde{t}}$ < 610 GeV.
Additional limits are set on the pair-production of massive colour-octet
resonances.
