The lower critical field Hcl in ultraclean URu 2Si2 single crystals (Tc 1.4K) with residual resistivity ratio exceeding 700 is precisely determined by the positional dependence of the local magnetic induction measured down to 55mK. We show that the whole Hcl(T) for H || a can be explained by the two gaps with line and point nodes. In contrast, for H || c we find a distinct kink in the slope of Hc1 at 1.2 K, which cannot be accounted for by the two gaps. This outstanding anomaly demonstrates a highly unusual superconducting state embedded in the hidden order state of URu2Si2 possibly related to the time reversal symmetry breaking. © Published under licence by IOP Publishing Ltd.